crates/hub/src/web/proposals.rs at 8f0efa0729b0 · andymccall/oxygenhub

# 8f0efa0729b0 oxygenhub / crates / hub / src / web / proposals.rs
78.6 KiB · Rust · last changed Drafts stream into the editor as the assistant writes them 19 days ago source blame history raw
//! Proposal pages (hub spec §7): list, new, detail with conversation,
//! changes and files, comments anchored to atoms, reviews, landing.

use super::history::{render_files, FileRows};
use super::settings::{csrf, require};
use super::{filters, lookup, lookup_role, Error, Page, RepoShell, Shell};
use crate::auth::{Access, Role, Viewer};
use crate::db::{self, accounts, proposals as pdb};
use crate::render::{self, diff};
use crate::repos::proposals::{self as pl, Projection, Source};
use crate::repos::view::{self, ChangeView, ConflictView};
use crate::repos::RepoName;
use crate::Shared;
use askama::Template;
use axum::extract::{Form, Path, Query, State};
use axum::response::{IntoResponse, Redirect, Response};
use hub_api::{Approval, ProposalSource, ProposalState};
use oxy_core::hash::ChangeHash;
use serde::Deserialize;
use std::collections::{BTreeMap, HashMap};

// ------------------------------------------------------------------ list

#[derive(Template)]
#[template(path = "proposals.html")]
pub struct ProposalsPage {
    shell: Shell,
    repo: RepoShell,
    rows: Vec<pdb::ProposalRow>,
    filter: String,
    counts: (usize, usize, usize),
    bookmarks: Vec<String>,
    q: String,
    sort: String,
    pager: super::Pager,
    labels: std::collections::HashMap<i64, Vec<db::issues::Label>>,
}

impl ProposalsPage {
    fn labels_of(&self, id: &i64) -> &[db::issues::Label] {
        self.labels.get(id).map(Vec::as_slice).unwrap_or(&[])
    }
}

#[derive(Deserialize)]
pub struct ListQuery {
    state: Option<String>,
    q: Option<String>,
    sort: Option<String>,
    page: Option<usize>,
}

/// The list's sort orders.
pub const SORTS: &[(&str, &str)] = &[("updated", "recently updated"), ("newest", "newest"), ("oldest", "oldest")];

pub async fn list(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name)): Path<(String, String)>,
    Query(q): Query<ListQuery>,
) -> Result<Page<ProposalsPage>, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposals"), &viewer);
    let (repo, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let all = pdb::list(&app.db, row.id, &[]).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    let counts = (
        all.iter().filter(|p| p.is_open()).count(),
        all.iter().filter(|p| p.state == "landed").count(),
        all.iter().filter(|p| p.state == "closed").count(),
    );
    let filter = q.state.unwrap_or_else(|| "open".into());
    let mut labels: std::collections::HashMap<i64, Vec<db::issues::Label>> = std::collections::HashMap::new();
    for (id, l) in db::issues::labels_by_proposal(&app.db, row.id).await.map_err(|e| Error::from_db(shell.clone(), e))? {
        labels.entry(id).or_default().push(l);
    }
    // `author:bob label:ui target:main words…`
    let qtext = q.q.clone().unwrap_or_default();
    let (mut authors, mut wanted, mut targets, mut words) = (vec![], vec![], vec![], vec![]);
    for tok in qtext.split_whitespace() {
        match tok.split_once(':') {
            Some(("author", v)) => authors.push(v.to_lowercase()),
            Some(("label", v)) => wanted.push(v.to_lowercase()),
            Some(("target", v)) => targets.push(v.to_string()),
            _ => words.push(tok.to_lowercase()),
        }
    }
    let mut rows: Vec<pdb::ProposalRow> = all
        .into_iter()
        .filter(|p| match filter.as_str() {
            "open" => p.is_open(),
            "landed" => p.state == "landed",
            "closed" => p.state == "closed",
            _ => true,
        })
        .filter(|p| authors.is_empty() || authors.contains(&p.author.to_lowercase()))
        .filter(|p| targets.is_empty() || targets.contains(&p.target))
        .filter(|p| wanted.iter().all(|w| labels.get(&p.id).is_some_and(|ls| ls.iter().any(|l| l.name.to_lowercase() == *w))))
        .filter(|p| words.iter().all(|w| p.title.to_lowercase().contains(w) || p.body.to_lowercase().contains(w)))
        .collect();
    let sort = q.sort.filter(|s| SORTS.iter().any(|(k, _)| k == s)).unwrap_or_else(|| "updated".into());
    match sort.as_str() {
        "newest" => rows.sort_by_key(|p| std::cmp::Reverse(p.number)),
        "oldest" => rows.sort_by_key(|p| p.number),
        _ => rows.sort_by_key(|p| std::cmp::Reverse(p.updated_ms)),
    }
    let pager = super::Pager::new(rows.len(), q.page, &[("state", &filter), ("q", &qtext), ("sort", &sort)]);
    let rows = pager.slice(rows);
    let bookmarks = app
        .repos
        .read(&repo, |r, _| Ok(r.bookmarks()?.into_iter().map(|b| b.name).collect::<Vec<_>>()))
        .await
        .map_err(|e| Error::from_repo(shell.clone(), e))?;
    Ok(Page(ProposalsPage {
        shell,
        repo: RepoShell::new(&app, &row, "proposals").with_role(role),
        rows,
        filter,
        counts,
        bookmarks,
        q: qtext,
        sort,
        pager,
        labels,
    }))
}

// ------------------------------------------------------------------- new

#[derive(Template)]
#[template(path = "proposal_new.html")]
pub struct NewProposalPage {
    shell: Shell,
    repo: RepoShell,
    bookmarks: Vec<String>,
    source: String,
    target: String,
    error: Option<String>,
    /// Preview: the changes the proposal would add.
    preview: Vec<ChangeView>,
    conflicted: bool,
    /// What the form holds so far (after a failed open, or a draft).
    title: String,
    body: String,
    /// AI assistants that may draft the description (hub spec §13.4).
    assistants: Vec<String>,
}

#[derive(Deserialize)]
pub struct NewQuery {
    source: Option<String>,
    target: Option<String>,
}

/// `owner/name:bookmark` for a fork, else a bookmark of this repository.
/// A proposal's source: a bookmark of this repository by name (which may
/// hold `/`, as `feature/16-hud` does), or `owner/name:bookmark` of a fork;
/// `owner/name:bookmark` naming this repository is its own bookmark.
fn parse_source(app: &Shared, repo: &RepoName, source: &str) -> Option<(Option<RepoName>, String)> {
    let plain = |b: &str| !b.is_empty() && !b.chars().any(|c| c.is_control() || c == ':');
    if let Some((slug, bookmark)) = source.split_once(':') {
        let fork = RepoName::parse(slug)?;
        if !plain(bookmark) {
            return None;
        }
        if fork == *repo {
            return Some((None, bookmark.to_string()));
        }
        if !app.repos.exists(&fork) {
            return None;
        }
        return Some((Some(fork), bookmark.to_string()));
    }
    plain(source).then(|| (None, source.to_string()))
}

async fn preview_for(
    app: &Shared,
    repo: &RepoName,
    target: &str,
    source: &str,
) -> Result<(Vec<ChangeView>, bool), crate::repos::RepoError> {
    let Some((fork, bookmark)) = parse_source(app, repo, source) else { return Ok((vec![], false)) };
    let target = target.to_string();
    let fork_dir = fork.as_ref().map(|f| app.repos.dir(f));
    app.repos
        .read(repo, move |r, cache| {
            let projection = match &fork_dir {
                Some(dir) => {
                    let fork_repo = oxy_core::repo::Repo::open(dir)?;
                    let heads = fork_repo.bookmarks()?.into_iter().find(|b| b.name == bookmark).map(|b| b.heads).unwrap_or_default();
                    pl::project(r, cache, &target, Source::Fork { fork: &fork_repo, heads })?
                }
                None => {
                    let heads = r.bookmarks()?.into_iter().find(|b| b.name == bookmark).map(|b| b.heads).unwrap_or_default();
                    pl::project(r, cache, &target, Source::Bookmark(heads))?
                }
            };
            Ok((projection.changes, projection.conflicted))
        })
        .await
}

pub async fn new_form(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name)): Path<(String, String)>,
    Query(q): Query<NewQuery>,
) -> Result<Page<NewProposalPage>, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposals/new"), &viewer);
    require(&viewer, &shell)?;
    let (repo, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let bookmarks = app
        .repos
        .read(&repo, |r, _| Ok(r.bookmarks()?.into_iter().map(|b| b.name).collect::<Vec<_>>()))
        .await
        .map_err(|e| Error::from_repo(shell.clone(), e))?;
    let target = q.target.unwrap_or_else(|| row.default_bookmark.clone());
    let source = q.source.unwrap_or_default();
    let (preview, conflicted) =
        if source.is_empty() { (vec![], false) } else { preview_for(&app, &repo, &target, &source).await.unwrap_or((vec![], false)) };
    let assistants = if preview.is_empty() { vec![] } else { assistant_names(&app, &row).await };
    Ok(Page(NewProposalPage {
        shell,
        repo: RepoShell::new(&app, &row, "proposals").with_role(role),
        bookmarks,
        source,
        target,
        error: None,
        preview,
        conflicted,
        title: String::new(),
        body: String::new(),
        assistants,
    }))
}

#[derive(Deserialize)]
pub struct NewForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    title: String,
    #[serde(default)]
    body: String,
    target: String,
    source: String,
    #[serde(default)]
    draft: Option<String>,
    /// For `/proposals/new/draft`: which assistant writes the description.
    #[serde(default)]
    assistant: String,
}

/// Open a proposal from a form or the API: validate, create, index, notify.
#[allow(clippy::too_many_arguments)]
pub async fn open_proposal(
    app: &Shared,
    repo: &RepoName,
    row: &db::repos::RepoRow,
    me: &accounts::Account,
    title: &str,
    body: &str,
    target: &str,
    source: &str,
    draft: bool,
) -> Result<pdb::ProposalRow, String> {
    if title.trim().is_empty() {
        return Err("Give the proposal a title.".into());
    }
    let bookmarks =
        app.repos.read(repo, |r, _| Ok(r.bookmarks()?.into_iter().map(|b| b.name).collect::<Vec<_>>())).await.map_err(|e| e.to_string())?;
    if !bookmarks.iter().any(|b| b == target) {
        return Err("Pick a target bookmark of this repository.".into());
    }
    let Some((fork, bookmark)) = parse_source(app, repo, source.trim()) else {
        return Err("The source is a bookmark of this repository, or owner/name:bookmark of a fork.".into());
    };
    if fork.is_none() && !bookmarks.contains(&bookmark) {
        return Err(format!("There is no bookmark {bookmark} in this repository."));
    }
    if fork.is_none() && bookmark == target {
        return Err("The source and the target are the same bookmark.".into());
    }
    let (preview, _) = preview_for(app, repo, target, source.trim()).await.map_err(|e| e.to_string())?;
    if preview.is_empty() {
        return Err("The source adds nothing to the target.".into());
    }
    let source_repo_id = match &fork {
        Some(fk) => db::repos::get(&app.db, &fk.owner, &fk.name).await.map_err(|e| e.to_string())?.map(|r| r.id),
        None => None,
    };
    let created = pdb::create(
        &app.db,
        pdb::NewProposal {
            repo_id: row.id,
            title: title.trim(),
            body: body.trim(),
            author_id: Some(me.id),
            author: &me.username,
            draft,
            target,
            source_kind: if fork.is_some() { "fork" } else { "bookmark" },
            source_repo_id,
            source_bookmark: &bookmark,
            source_changes: "",
        },
    )
    .await
    .map_err(|e| e.to_string())?;
    pdb::add_event(&app.db, created.id, &me.username, "opened", "").await.ok();
    accounts::audit(&app.db, Some(me), "proposal.opened", &format!("{}#{}", row.slug(), created.number), title).await.ok();
    db::notify::index(&app.db, "proposal", row.id, created.id, created.number, &created.title, &created.body).await.ok();
    let url = format!("/{}/proposal/{}", row.slug(), created.number);
    crate::notify::deliver(
        app,
        crate::notify::Event {
            kind: "proposal.opened",
            title: format!("{}#{}: {}", row.slug(), created.number, created.title),
            url,
            actor: me,
            repo_id: row.id,
            thread: Some(("proposal", created.id)),
            mention_text: body,
            direct: vec![],
        },
    )
    .await;
    crate::hooks::emit(
        app,
        row,
        "proposal.opened",
        &me.username,
        serde_json::json!({ "number": created.number, "title": created.title, "target": target, "source": source }),
    )
    .await;
    Ok(created)
}

pub async fn create(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name)): Path<(String, String)>,
    Form(f): Form<NewForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposals/new"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (repo, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    match open_proposal(&app, &repo, &row, &me.account, &f.title, &f.body, &f.target, &f.source, f.draft.is_some()).await {
        Ok(created) => Ok(Redirect::to(&format!("/{owner}/{name}/proposal/{}", created.number)).into_response()),
        Err(msg) => {
            let bookmarks =
                app.repos.read(&repo, |r, _| Ok(r.bookmarks()?.into_iter().map(|b| b.name).collect::<Vec<_>>())).await.unwrap_or_default();
            Ok(Page(NewProposalPage {
                shell,
                repo: RepoShell::new(&app, &row, "proposals").with_role(role),
                bookmarks,
                source: f.source.clone(),
                target: f.target.clone(),
                error: Some(msg),
                preview: vec![],
                conflicted: false,
                title: f.title.clone(),
                body: f.body.clone(),
                assistants: vec![],
            })
            .into_response())
        }
    }
}

// ---------------------------------------------------------------- detail

/// A comment placed on a diff row, or general.
pub struct CommentView {
    pub row: pdb::CommentRow,
    pub body_html: String,
    pub line: Option<usize>,
}

/// One entry of a proposal's conversation, in time order: what kind it
/// is and its index in `comments`, `reviews` or `events`.
pub struct Entry {
    pub kind: &'static str,
    pub index: usize,
}

pub struct ReviewView {
    pub row: pdb::ReviewRow,
    pub body_html: String,
    pub sealed: bool,
}

/// Everything the detail page and the API need, computed once under the lock.
pub struct Loaded {
    pub row: pdb::ProposalRow,
    pub changes: Vec<ChangeView>,
    pub hashes: Vec<ChangeHash>,
    pub heads: Vec<ChangeHash>,
    pub target_heads: Vec<ChangeHash>,
    pub state: String,
    pub target_state: String,
    pub conflicted: bool,
    pub conflicts: Vec<ConflictView>,
    pub files: Vec<FileRows>,
    /// The per-file hunks and bases behind `files`, to render again with other options.
    pub diffs: Vec<oxy_core::repo::FileDiff>,
    pub bases: std::collections::BTreeMap<String, Vec<u8>>,
    /// Atom per (path, new line number) of the projected state.
    pub atoms: HashMap<(String, usize), (String, u32)>,
    pub sealing_keys: Vec<String>,
    pub touched: Vec<String>,
    pub owners: Vec<String>,
    pub landed_already: bool,
    /// Whether its source has any changes at all (#141): an open proposal
    /// whose source has changes, none of them missing from the target, was
    /// landed by some other route.
    pub source_has_changes: bool,
}

/// Compute the projection and everything derived from it.
pub async fn load(app: &Shared, repo: &RepoName, row: pdb::ProposalRow) -> Result<Loaded, crate::repos::RepoError> {
    let fork_dir = match (row.source_kind.as_str(), row.source_repo_id) {
        ("fork", Some(id)) => {
            db::repos::get_by_id(&app.db, id).await.ok().flatten().and_then(|r| RepoName::new(&r.owner, &r.name)).map(|n| app.repos.dir(&n))
        }
        _ => None,
    };
    let r2 = row.clone();
    let loaded = app
        .repos
        .read(repo, move |r, cache| {
            let source = match (r2.source_kind.as_str(), &fork_dir) {
                ("changes", _) => Source::Changes(r2.source_changes().iter().filter_map(|h| ChangeHash::from_hex(h)).collect()),
                ("fork", Some(dir)) => {
                    let fork_repo = oxy_core::repo::Repo::open(dir)?;
                    let heads =
                        fork_repo.bookmarks()?.into_iter().find(|b| b.name == r2.source_bookmark).map(|b| b.heads).unwrap_or_default();
                    // Bring the fork's changes over now, so the projection below can read them.
                    let fork_state = fork_repo.load_state(&heads)?;
                    let missing: Vec<ChangeHash> = fork_state.changes().map(|(h, _)| *h).filter(|h| !r.store().has(h)).collect();
                    if !missing.is_empty() {
                        r.import_bundle(&fork_repo.bundle_for(&missing)?, r.current_policy()?.is_some())?;
                    }
                    Source::Changes(heads)
                }
                _ => {
                    let heads = r.bookmarks()?.into_iter().find(|b| b.name == r2.source_bookmark).map(|b| b.heads).unwrap_or_default();
                    Source::Bookmark(heads)
                }
            };
            let source_has_changes = match &source {
                Source::Changes(h) | Source::Bookmark(h) | Source::Fork { heads: h, .. } => !h.is_empty(),
            };
            let p: Projection = pl::project(r, cache, &r2.target, source)?;
            let target_loaded = cache.load(r, &p.target_heads)?;
            let files = render_files(&p.files, &p.bases);
            let mut atoms = HashMap::new();
            for f in &files {
                for l in &f.lines {
                    if let Some(n) = l.new_no {
                        if let Some((h, i)) = pl::atom_at(&p.loaded, &f.path, n as usize) {
                            atoms.insert((f.path.clone(), n as usize), (h.to_hex(), i));
                        }
                    }
                }
            }
            let touched: Vec<String> = p.files.iter().map(|f| f.path.clone()).collect();
            let owners = pl::owners_for(&target_loaded, &touched);
            let sealing = pl::sealing_keys(r, &p.hashes)?.into_iter().map(|k| k.to_hex()).collect();
            let landed_already = !p.hashes.is_empty() && p.hashes.iter().all(|h| target_loaded.state.contains(h));
            // A landed proposal's changes are in its target now: it shows
            // the ones it landed, as recorded when it landed.
            let (changes, hashes) = if r2.state == "landed" && p.hashes.is_empty() {
                let hashes: Vec<ChangeHash> = r2.projected_changes().iter().filter_map(|h| ChangeHash::from_hex(h)).collect();
                let labels = HashMap::new();
                let changes = hashes
                    .iter()
                    .filter_map(|h| Some(view::change_view_pub(r, h, &r.store().get_change_meta(h).ok()?, false, &labels)))
                    .collect();
                (changes, hashes)
            } else {
                (p.changes, p.hashes)
            };
            Ok(Loaded {
                row: r2,
                changes,
                hashes,
                heads: p.heads,
                target_heads: p.target_heads.clone(),
                state: p.state.to_hex(),
                target_state: p.target_state.to_hex(),
                conflicted: p.conflicted,
                conflicts: p.conflicts,
                files,
                diffs: p.files.clone(),
                bases: p.bases.clone(),
                atoms,
                sealing_keys: sealing,
                touched,
                owners,
                landed_already,
                source_has_changes,
            })
        })
        .await?;
    // Landed by another route (#141): `oxy proposal land` from a client (a
    // repository with a trust policy needs it), or the work merged and
    // pushed by hand. Everything it proposes is in its target, so it is
    // landed, not open with nothing to land.
    let mut loaded = loaded;
    if loaded.row.is_open()
        && loaded.source_has_changes
        && loaded.hashes.is_empty()
        && pdb::set_landed(&app.db, loaded.row.id, &loaded.target_state, "", "push").await.is_ok()
    {
        loaded.row.state = "landed".into();
        loaded.row.landed_via = "push".into();
        loaded.row.landed_state = loaded.target_state.clone();
        return Ok(loaded);
    }
    // Remember the projection for the list, the API and other proposals'
    // stacking checks, while the proposal is open: a landed one keeps what
    // it landed.
    if !loaded.row.is_open() {
        return Ok(loaded);
    }
    let heads_csv = loaded.heads.iter().map(|h| h.to_hex()).collect::<Vec<_>>().join(",");
    let changes_csv = loaded.hashes.iter().map(|h| h.to_hex()).collect::<Vec<_>>().join(",");
    pdb::set_projection(&app.db, loaded.row.id, &loaded.state, &heads_csv, &loaded.target_state, &changes_csv, loaded.conflicted)
        .await
        .ok();
    Ok(loaded)
}

/// After a push moved `bookmark`: open proposals into it whose work it now
/// holds are marked landed, by the pusher (#141).
pub async fn settle_after_push(app: &Shared, row: &db::repos::RepoRow, bookmark: &str, actor: &str) {
    let Some(repo) = RepoName::new(&row.owner, &row.name) else { return };
    let Ok(open) = pdb::list(&app.db, row.id, &["open", "draft"]).await else { return };
    for p in open.into_iter().filter(|p| p.target == bookmark) {
        let id = p.id;
        let number = p.number;
        if let Ok(l) = load(app, &repo, p).await {
            if l.row.state == "landed" && l.row.landed_by.is_empty() {
                pdb::set_landed(&app.db, id, &l.target_state, actor, "push").await.ok();
            } else if l.row.is_open() && !l.hashes.is_empty() && crate::flow::enabled(app, row) {
                // The target moved, so the proposal's projected state is
                // new and its checks would be for an older one (#134): run
                // the pipeline on it, once.
                let ran: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM flow_runs WHERE repo_id = ? AND state = ?")
                    .bind(row.id)
                    .bind(&l.state)
                    .fetch_one(&app.db)
                    .await
                    .unwrap_or(1);
                if ran == 0 {
                    let label = format!("proposal/{number}");
                    match crate::flow::start_run_scoped(app, row, &label, &l.state, &l.heads, actor, "proposal", None).await {
                        Ok(Some(n)) => tracing::info!("proposal {number}: its target moved; run #{n} checks its new projected state"),
                        Ok(None) => {}
                        Err(e) => tracing::warn!("proposal {number}: a run of its new projected state did not start: {e}"),
                    }
                }
            }
        }
    }
}

/// Reviews, approvals and blockers.
pub struct Verdict {
    pub reviews: Vec<ReviewView>,
    pub approvals: Vec<Approval>,
    pub blockers: Vec<String>,
    pub depends_on: Vec<i64>,
    pub requirements: pdb::Requirements,
}

pub async fn verdict(app: &Shared, loaded: &Loaded, repo_id: i64) -> Result<Verdict, sqlx::Error> {
    let rows = pdb::reviews(&app.db, loaded.row.id).await?;
    let links = accounts::identity_accounts(&app.db).await?;
    let sealed_accounts: Vec<String> = links.iter().filter(|(k, _)| loaded.sealing_keys.contains(k)).map(|(_, u)| u.clone()).collect();
    // Latest verdict per reviewer.
    let mut latest: BTreeMap<String, &pdb::ReviewRow> = BTreeMap::new();
    for r in rows.iter().filter(|r| r.via.is_empty()) {
        // An assistant's answer is never the person's own verdict.
        latest.insert(r.author.clone(), r);
    }
    let mut approvals = Vec::new();
    for (who, r) in &latest {
        if r.verdict == "approve" {
            let sealed = sealed_accounts.contains(who);
            let key = links.iter().find(|(k, u)| u == who && loaded.sealing_keys.contains(k)).map(|(k, _)| k.clone());
            approvals.push(Approval { account: who.clone(), sealed, key });
        }
    }
    let reviews = rows
        .iter()
        .map(|r| ReviewView {
            row: r.clone(),
            body_html: render::markdown::render(&r.body, "/", "/"),
            sealed: r.verdict == "approve" && sealed_accounts.contains(&r.author),
        })
        .collect();
    let requirements = pdb::requirements(&app.db, repo_id).await?;
    let mut blockers = Vec::new();
    // Only an open proposal can be held back.
    if !loaded.row.is_open() {
        return Ok(Verdict { reviews, approvals, blockers, depends_on: vec![], requirements });
    }
    if loaded.row.state == "draft" {
        blockers.push("the proposal is a draft".into());
    }
    if loaded.hashes.is_empty() {
        blockers.push("the proposal adds no changes".into());
    }
    let sealed_count = approvals.iter().filter(|a| a.sealed).count() as i64;
    if sealed_count < requirements.required_approvals {
        blockers.push(format!("{sealed_count} of {} required sealed approvals", requirements.required_approvals));
    }
    if requirements.require_owners {
        let missing: Vec<&String> = loaded.owners.iter().filter(|o| !approvals.iter().any(|a| a.sealed && &a.account == *o)).collect();
        if !missing.is_empty() {
            blockers.push(format!("code owners still to approve: {}", missing.iter().map(|s| s.as_str()).collect::<Vec<_>>().join(", ")));
        }
    }
    if loaded.conflicted && !requirements.allow_conflicts {
        blockers.push("landing would carry conflicts, which this repository refuses".into());
    }
    let required = db::hooks::required_checks(&app.db, repo_id).await?;
    if !required.is_empty() {
        let checks = db::hooks::checks_for_state(&app.db, repo_id, &loaded.state).await?;
        let missing: Vec<String> =
            required.iter().filter(|n| !checks.iter().any(|c| &c.name == *n && c.status == "passed")).cloned().collect();
        if !missing.is_empty() {
            blockers.push(format!("required checks not passed on the projected state: {}", missing.join(", ")));
        }
    }
    let requesting: Vec<&String> = latest.iter().filter(|(_, r)| r.verdict == "changes").map(|(who, _)| who).collect();
    if !requesting.is_empty() {
        blockers.push(format!("changes requested by {}", requesting.iter().map(|s| s.as_str()).collect::<Vec<_>>().join(", ")));
    }
    // Stacking: another open, earlier proposal whose changes this one includes.
    let mut depends_on = Vec::new();
    for other in pdb::list(&app.db, repo_id, &["open", "draft"]).await? {
        if other.id == loaded.row.id || other.number > loaded.row.number {
            continue;
        }
        let theirs = other.projected_changes();
        if !theirs.is_empty() && theirs.iter().all(|h| loaded.hashes.iter().any(|m| m.to_hex() == *h)) {
            depends_on.push(other.number);
        }
    }
    if !depends_on.is_empty() {
        blockers.push(format!("depends on {}", depends_on.iter().map(|n| format!("#{n}")).collect::<Vec<_>>().join(", ")));
    }
    Ok(Verdict { reviews, approvals, blockers, depends_on, requirements })
}

#[derive(Template)]
#[template(path = "proposal.html")]
pub struct ProposalPage {
    shell: Shell,
    repo: RepoShell,
    p: pdb::ProposalRow,
    /// Issues it closes, from its description and its changes.
    closes: Vec<super::chain::Link>,
    /// Projects the viewer may add it to.
    project_choices: Option<Vec<db::projects::Project>>,
    /// Comments (not anchored to a line), reviews and events, oldest first.
    timeline: Vec<Entry>,
    /// The viewer may set labels (triage or above).
    can_triage: bool,
    body_html: String,
    tab: String,
    changes: Vec<ChangeView>,
    files: Vec<FileRows>,
    diffs: Vec<oxy_core::repo::FileDiff>,
    bases: std::collections::BTreeMap<String, Vec<u8>>,
    /// Whitespace-only changes are hidden (`?w=1`).
    ignore_ws: bool,
    conflicts: Vec<ConflictView>,
    conflicted: bool,
    comments: Vec<CommentView>,
    /// Anchored comments by (path, current line).
    placed: HashMap<(String, usize), Vec<usize>>,
    outdated: Vec<usize>,
    reviews: Vec<ReviewView>,
    approvals: Vec<Approval>,
    blockers: Vec<String>,
    depends_on: Vec<i64>,
    events: Vec<pdb::EventRow>,
    owners: Vec<String>,
    requirements: pdb::Requirements,
    landed_already: bool,
    can_edit: bool,
    /// The landed proposal's source bookmark, when it is this repository's,
    /// still there, and the viewer may delete it (oxygenhub#86).
    deletable_source: Option<String>,
    can_land: bool,
    hub_can_land: bool,
    notice: Option<String>,
    error: Option<String>,
    heads: Vec<String>,
    state_hash: String,
    source_label: String,
    api_url: String,
    labels: Vec<db::issues::Label>,
    all_labels: Vec<db::issues::Label>,
    checks: Vec<db::hooks::Check>,
    required_checks: Vec<String>,
    /// Projects this proposal is on that the viewer may see, with the column.
    projects: Vec<(db::projects::Project, String)>,
    /// Asked to review and not yet reviewing.
    requested: Vec<String>,
    /// Who can be asked to review, for the sidebar's menu (oxygenhub#84).
    reviewable: Vec<String>,
    /// The viewer may ask for reviews (the author, or a writer).
    can_request: bool,
    /// AI assistants the viewer may ask, by name (hub spec §13.4).
    assistants: Vec<String>,
    /// A description an assistant just drafted, for the editor.
    draft: Option<String>,
}

#[derive(Deserialize)]
pub struct DetailQuery {
    tab: Option<String>,
    /// What an action said, after it redirected here.
    #[serde(default)]
    notice: Option<String>,
    #[serde(default)]
    error: Option<String>,
    #[serde(default)]
    w: Option<String>,
}

/// The page assembler every action ends in; its arguments are the route
/// plus what to say, and a struct would only rename them.
#[allow(clippy::too_many_arguments)]
async fn detail(
    app: &Shared,
    shell: Shell,
    viewer: &Viewer,
    owner: &str,
    name: &str,
    number: i64,
    tab: String,
    notice: Option<String>,
    error: Option<String>,
) -> Result<Page<ProposalPage>, Error> {
    let (repo, row, role) = lookup(app, &shell, viewer, owner, name).await?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    let loaded = load(app, &repo, p).await.map_err(|e| Error::from_repo(shell.clone(), e))?;
    // A proposal whose changes all reached the target landed by another route.
    if loaded.landed_already && loaded.row.is_open() {
        pdb::set_state(&app.db, loaded.row.id, "landed", &loaded.target_state).await.ok();
        pdb::add_event(&app.db, loaded.row.id, "", "landed", "every change reached the target").await.ok();
    }
    let p = pdb::get(&app.db, row.id, number).await.map_err(|e| Error::from_db(shell.clone(), e))?.unwrap_or(loaded.row.clone());
    let v = verdict(app, &loaded, row.id).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    let comment_rows = pdb::comments(&app.db, loaded.row.id).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    let events = pdb::events(&app.db, loaded.row.id).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    // Place anchored comments at their atom's current line.
    let mut by_atom: HashMap<(String, String, u32), usize> = HashMap::new();
    for ((path, line), (h, i)) in &loaded.atoms {
        by_atom.insert((path.clone(), h.clone(), *i), *line);
    }
    let mut comments = Vec::new();
    let mut placed: HashMap<(String, usize), Vec<usize>> = HashMap::new();
    let mut outdated = Vec::new();
    for (idx, c) in comment_rows.into_iter().enumerate() {
        let line = if c.anchor_change.is_empty() {
            None
        } else {
            by_atom.get(&(c.path.clone(), c.anchor_change.clone(), c.anchor_index as u32)).copied()
        };
        if !c.anchor_change.is_empty() {
            match line {
                Some(l) => placed.entry((c.path.clone(), l)).or_default().push(idx),
                None => outdated.push(idx),
            }
        }
        comments.push(CommentView { body_html: render::markdown::render(&c.body, "/", "/"), row: c, line });
    }
    let mut changes = loaded.changes.clone();
    super::attribute(app, &mut changes.iter_mut().collect::<Vec<_>>()).await;
    let me = viewer.account();
    let can_edit = me.is_some_and(|a| Some(a.id) == p.author_id || role >= Role::Maintain);
    let deletable_source =
        if p.state == "landed" && p.source_kind == "bookmark" && role >= Role::Write && p.source_bookmark != row.default_bookmark {
            let b = p.source_bookmark.clone();
            app.repos
                .read(&repo, move |r, _| Ok(r.view()?.bookmarks.contains_key(&b)))
                .await
                .unwrap_or(false)
                .then(|| p.source_bookmark.clone())
        } else {
            None
        };
    let can_land = role >= Role::Write && p.is_open() && v.blockers.is_empty();
    let can_request = p.is_open() && me.is_some_and(|a| Some(a.id) == p.author_id || role >= Role::Write);
    let requested = pdb::review_requests(&app.db, p.id).await.unwrap_or_default();
    let mut reviewable: Vec<String> = if can_request {
        accounts::assignable(&app.db, row.id, &row.owner).await.unwrap_or_default().into_iter().filter(|u| *u != p.author).collect()
    } else {
        Vec::new()
    };
    for r in &requested {
        if !reviewable.iter().any(|x| x.eq_ignore_ascii_case(r)) {
            reviewable.push(r.clone());
        }
    }
    let assistants: Vec<String> = if (can_request || can_edit) && p.is_open() { assistant_names(app, &row).await } else { Vec::new() };
    let delegated = match viewer.account() {
        Some(a) => super::edit::delegated_identity(app, a.id).await.is_some(),
        None => false,
    };
    let hub_can_land = delegated || app.repos.read(&repo, |r, _| Ok(r.current_policy()?.is_none())).await.unwrap_or(false);
    let source_label = match p.source_kind.as_str() {
        "fork" => format!(
            "fork {}",
            db::repos::get_by_id(&app.db, p.source_repo_id.unwrap_or(0))
                .await
                .ok()
                .flatten()
                .map(|r| format!("{}:{}", r.slug(), p.source_bookmark))
                .unwrap_or_default()
        ),
        "changes" => format!("{} changes", p.source_changes().len()),
        _ => p.source_bookmark.clone(),
    };
    let projects = super::projects::placements_for(app, viewer, &row, p.number).await;
    let texts: Vec<String> = std::iter::once(p.body.clone()).chain(changes.iter().map(|c| format!("{}\n{}", c.title, c.body))).collect();
    let closes = super::chain::issues_closed_by(app, &row, &texts.iter().map(String::as_str).collect::<Vec<_>>()).await;
    let project_choices = super::projects::project_choices(app, viewer, &row, &projects).await;
    let mut dated: Vec<(i64, Entry)> = Vec::new();
    for (index, c) in comments.iter().enumerate() {
        if c.row.anchor_change.is_empty() {
            dated.push((c.row.created_ms, Entry { kind: "comment", index }));
        }
    }
    for (index, r) in v.reviews.iter().enumerate() {
        dated.push((r.row.created_ms, Entry { kind: "review", index }));
    }
    for (index, e) in events.iter().enumerate() {
        dated.push((e.at_ms, Entry { kind: "event", index }));
    }
    dated.sort_by_key(|(at, _)| *at);
    let timeline: Vec<Entry> = dated.into_iter().map(|(_, e)| e).collect();
    Ok(Page(ProposalPage {
        can_triage: role >= Role::Triage,
        timeline,
        closes,
        project_choices,
        projects,
        shell,
        repo: RepoShell::new(app, &row, "proposals").with_role(role).with_sky(app, &row).await,
        body_html: super::issues::markdown(app, &row, &row.default_bookmark, &p.body).await,
        p,
        tab,
        changes,
        files: loaded.files,
        diffs: loaded.diffs,
        bases: loaded.bases,
        ignore_ws: false,
        conflicts: loaded.conflicts,
        conflicted: loaded.conflicted,
        comments,
        placed,
        outdated,
        reviews: v.reviews,
        approvals: v.approvals,
        blockers: v.blockers,
        depends_on: v.depends_on,
        events,
        owners: loaded.owners,
        requirements: v.requirements,
        landed_already: loaded.landed_already,
        can_edit,
        deletable_source,
        can_land,
        hub_can_land,
        notice,
        error,
        heads: loaded.heads.iter().map(|h| h.to_hex()).collect(),
        state_hash: loaded.state.clone(),
        source_label,
        api_url: format!("{}/api/v1/repos/{owner}/{name}/proposals/{number}", app.config.base_url()),
        labels: db::issues::proposal_labels(&app.db, loaded.row.id).await.unwrap_or_default(),
        all_labels: db::issues::labels(&app.db, row.id).await.unwrap_or_default(),
        checks: db::hooks::checks_for_state(&app.db, row.id, &loaded.state).await.unwrap_or_default(),
        required_checks: db::hooks::required_checks(&app.db, row.id).await.unwrap_or_default(),
        requested,
        reviewable,
        assistants,
        draft: None,
        can_request,
    }))
}

/// Back to the proposal after an action, with what to say: a redirect, so
/// reloading the page (the checks script does) never repeats the action.
fn back(owner: &str, name: &str, number: i64, tab: &str, notice: Option<String>, error: Option<String>) -> Response {
    let mut url = format!("/{owner}/{name}/proposal/{number}?tab={tab}");
    if let Some(n) = notice {
        url.push_str(&format!("&notice={}", super::settings::urlencode(&n)));
    }
    if let Some(e) = error {
        url.push_str(&format!("&error={}", super::settings::urlencode(&e)));
    }
    Redirect::to(&url).into_response()
}

pub async fn show(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Query(q): Query<DetailQuery>,
) -> Result<Page<ProposalPage>, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let mut page =
        detail(&app, shell, &viewer, &owner, &name, number, q.tab.unwrap_or_else(|| "conversation".into()), q.notice, q.error).await?;
    if q.w.as_deref() == Some("1") {
        // Hide whitespace-only changes: the same hunks, rendered again.
        page.0.files =
            super::history::render_files_with(&page.0.diffs, &page.0.bases, crate::render::diff::Options { ignore_whitespace: true });
        page.0.ignore_ws = true;
    }
    Ok(page)
}

// ---------------------------------------------------------------- actions

#[derive(Deserialize)]
pub struct CommentForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    body: String,
    #[serde(default)]
    path: String,
    #[serde(default)]
    line: Option<usize>,
}

pub async fn comment(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<CommentForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (repo, row, _) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if f.body.trim().is_empty() {
        return Ok(back(&owner, &name, number, "conversation", None, Some("An empty comment says nothing.".into())));
    }
    let anchor = match (f.path.trim(), f.line) {
        ("", _) | (_, None) => None,
        (path, Some(line)) => {
            let loaded = load(&app, &repo, p.clone()).await.map_err(|e| Error::from_repo(shell.clone(), e))?;
            loaded.atoms.get(&(path.to_string(), line)).cloned()
        }
    };
    let tab = if anchor.is_some() { "files" } else { "conversation" };
    pdb::add_comment(
        &app.db,
        p.id,
        Some(me.account.id),
        &me.account.username,
        f.body.trim(),
        f.path.trim(),
        anchor.as_ref().map(|(h, i)| (h.as_str(), *i as i64)),
    )
    .await
    .map_err(|e| Error::from_db(shell.clone(), e))?;
    Ok(back(&owner, &name, number, tab, None, None))
}

#[derive(Deserialize)]
pub struct ReviewForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    verdict: String,
    #[serde(default)]
    body: String,
}

pub async fn review(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<ReviewForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (_, row, _) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if !matches!(f.verdict.as_str(), "comment" | "changes" | "approve") {
        return Err(Error::bad(shell, "a review is comment, changes or approve"));
    }
    if f.verdict == "approve" && Some(me.account.id) == p.author_id {
        return Ok(back(&owner, &name, number, "conversation", None, Some("You cannot approve your own proposal.".into())));
    }
    pdb::add_review(&app.db, p.id, me.account.id, &me.account.username, &f.verdict, f.body.trim())
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?;
    pdb::add_event(&app.db, p.id, &me.account.username, &format!("review.{}", f.verdict), "").await.ok();
    reviewed(&app, &row, &p, &me.account, &f.verdict).await;
    crate::hooks::emit(&app, &row, "review", &me.account.username, serde_json::json!({ "number": number, "verdict": f.verdict })).await;
    let notice = if f.verdict == "approve" {
        Some(format!(
            "Approval recorded. It counts once you seal the changes: oxy seal --proposal {}/{owner}/{name}/proposal/{number}",
            app.config.base_url()
        ))
    } else {
        None
    };
    Ok(back(&owner, &name, number, "conversation", notice, None))
}

#[derive(Deserialize)]
pub struct EditForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    title: String,
    #[serde(default)]
    body: String,
    target: String,
}

pub async fn edit(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<EditForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (_, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if Some(me.account.id) != p.author_id && role < Role::Maintain {
        return Err(Error::not_found(shell));
    }
    let target = if crate::repos::names::valid_segment(f.target.trim()) { f.target.trim() } else { &p.target };
    pdb::edit(&app.db, p.id, f.title.trim(), f.body.trim(), target).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    pdb::add_event(&app.db, p.id, &me.account.username, "edited", "").await.ok();
    Ok(back(&owner, &name, number, "conversation", Some("Saved.".into()), None))
}

#[derive(Deserialize)]
pub struct StateForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    action: String,
}

pub async fn state(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<StateForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (_, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if Some(me.account.id) != p.author_id && role < Role::Triage {
        return Err(Error::not_found(shell));
    }
    let new_state = match (f.action.as_str(), p.state.as_str()) {
        ("close", "open" | "draft") => "closed",
        ("reopen", "closed") => "open",
        ("ready", "draft") => "open",
        ("draft", "open") => "draft",
        _ => return Err(Error::bad(shell, "that transition is not possible")),
    };
    pdb::set_state(&app.db, p.id, new_state, "").await.map_err(|e| Error::from_db(shell.clone(), e))?;
    pdb::add_event(&app.db, p.id, &me.account.username, new_state, "").await.ok();
    crate::hooks::emit(&app, &row, &format!("proposal.{new_state}"), &me.account.username, serde_json::json!({ "number": number })).await;
    Ok(back(&owner, &name, number, "conversation", None, None))
}

pub async fn resolve_comment(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number, id)): Path<(String, String, i64, i64)>,
    Form(f): Form<super::session::CsrfForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf, &shell)?;
    let (_, row, _) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    let current: Option<bool> = sqlx::query_scalar("SELECT resolved FROM proposal_comments WHERE id = ? AND proposal_id = ?")
        .bind(id)
        .bind(p.id)
        .fetch_optional(&app.db)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?;
    if let Some(r) = current {
        pdb::set_comment_resolved(&app.db, id, !r).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    }
    Ok(back(&owner, &name, number, "files", None, None))
}

/// Land from the hub: only when the repository has no trust policy (the
/// hub never signs a reference update the policy would have to admit).
pub async fn land(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<super::session::CsrfForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf, &shell)?;
    let (repo, row, _) = lookup_role(&app, &shell, &viewer, &owner, &name, Access::Write).await?;
    match land_as(&app, &repo, &row, &me.account, number, "web", false).await {
        Ok(_) => Ok(back(&owner, &name, number, "conversation", Some("Landed.".into()), None)),
        Err(Landing::NotFound) => Err(Error::not_found(shell)),
        Err(Landing::Refused(m)) => Ok(back(&owner, &name, number, "conversation", None, Some(m))),
    }
}

/// Why a proposal did not land.
pub enum Landing {
    NotFound,
    Refused(String),
}

/// Land proposal `number` as `me` (hub spec §8.4), who has write access:
/// refused while it is not open or has blockers. Moves the target bookmark
/// (attested by the hub key on `me`'s behalf when they delegated to it),
/// then records, announces and audits the landing, saying how it was done
/// (`via`: `web`, or `api (token NAME)`). `as_hub` signs with the hub's own
/// key rather than `me`'s delegation (Diffusion's auto-land). Returns the
/// new state.
pub async fn land_as(
    app: &Shared,
    repo: &RepoName,
    row: &db::repos::RepoRow,
    me: &accounts::Account,
    number: i64,
    via: &str,
    as_hub: bool,
) -> Result<String, Landing> {
    let (owner, name) = (row.owner.clone(), row.name.clone());
    let refused = |e: String| Landing::Refused(e);
    let p = pdb::get(&app.db, row.id, number).await.map_err(|e| refused(e.to_string()))?.ok_or(Landing::NotFound)?;
    let loaded = load(app, repo, p.clone()).await.map_err(|e| refused(e.to_string()))?;
    let v = verdict(app, &loaded, row.id).await.map_err(|e| refused(e.to_string()))?;
    if !p.is_open() {
        return Err(refused(format!("Cannot land: the proposal is {}", p.state)));
    }
    if !v.blockers.is_empty() {
        return Err(refused(format!("Cannot land: {}", v.blockers.join("; "))));
    }
    let target = p.target.clone();
    let heads = loaded.heads.clone();
    // With a delegation the landing is attested by the hub key on the
    // user's behalf, which a policy accepts when it lets the user update
    // the target (spec §14.5); without one, only a policy-free repository
    // can be landed here.
    let signer = if as_hub { super::edit::hub_signer(app) } else { super::edit::signer_for(app, me.id).await };
    let result = match signer {
        Ok(signer) => crate::repos::edits::move_bookmark(&app.repos, repo, target.clone(), heads.clone(), signer).await.map(|_| pl::state_ref(&heads).to_hex()),
        Err(why) => {
            app.repos
                .write(repo, move |r, _| {
                    if r.current_policy()?.is_some() {
                        return Err(crate::repos::RepoError::Oxy(oxy_core::repo::RepoError::Msg(format!(
                            "this repository has a trust policy, so the landing must be signed by a key it authorises. Land from a client with oxy proposal land, or delegate to the hub. {why}"
                        ))));
                    }
                    r.bookmark_set(&target, &heads)?;
                    Ok(pl::state_ref(&heads).to_hex())
                })
                .await
        }
    };
    let state = result.map_err(|e| refused(e.to_string()))?;
    pdb::set_landed(&app.db, p.id, &state, &me.username, via).await.map_err(|e| refused(e.to_string()))?;
    let how = if v.approvals.is_empty() { format!("{via}, with no approval") } else { via.to_string() };
    pdb::add_event(&app.db, p.id, &me.username, "landed", &how).await.ok();
    crate::hooks::emit(
        app,
        row,
        "proposal.landed",
        &me.username,
        serde_json::json!({ "number": number, "target": p.target, "state": state }),
    )
    .await;
    crate::notify::deliver(
        app,
        crate::notify::Event {
            kind: "proposal.landed",
            title: format!("{owner}/{name}#{number}: {} landed", p.title),
            url: format!("/{owner}/{name}/proposal/{number}"),
            actor: me,
            repo_id: row.id,
            thread: Some(("proposal", p.id)),
            mention_text: "",
            direct: p.author_id.into_iter().collect(),
        },
    )
    .await;
    if p.target == row.default_bookmark {
        let messages: Vec<(String, String)> = loaded.changes.iter().map(|c| (c.hash.clone(), format!("{}\n{}", c.title, c.body))).collect();
        super::issues::close_from_messages(app, row, &messages).await;
    }
    accounts::audit(&app.db, Some(me), "proposal.landed", &format!("{owner}/{name}#{number}"), &how).await.ok();
    db::repos::record_push(
        &app.db,
        row.id,
        Some((me.id, me.username.as_str())),
        &[db::repos::PushOutcome {
            reference: p.target.clone(),
            ok: true,
            reason: format!("landed #{number} ({how})"),
            old_state: loaded.target_state.clone(),
            new_state: state.clone(),
            heads: loaded.heads.len() as i64,
            changes: loaded.hashes.len() as i64,
        }],
    )
    .await
    .ok();
    // The target moved: its other open proposals are checked again (#134).
    settle_after_push(app, row, &p.target, &me.username).await;
    // A landing on the default bookmark closes the issues its changes (and
    // its description) say they close, as a push there would.
    if p.target == row.default_bookmark {
        let body = (format!("proposal #{number}"), p.body.clone());
        crate::web::issues::close_from_arrived(app, row, loaded.target_heads.clone(), loaded.heads.clone(), Some(body)).await;
    }
    // Diffusion (#150): a landing moves the target as a push would, so the
    // pin index follows it, and the consumers of a moved default bookmark
    // are bumped.
    let heads = loaded.heads.clone();
    let moved = vec![(p.target.clone(), state.clone(), heads.clone())];
    crate::diffusion::after_push(app, row, &moved).await;
    if p.target == row.default_bookmark {
        let (app, row) = (app.clone(), row.clone());
        tokio::spawn(async move { crate::diffusion::propagate(&app, &row, heads, false).await });
    }
    Ok(state)
}

#[derive(Deserialize)]
pub struct LabelsForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    #[serde(default)]
    label: Vec<i64>,
}

pub async fn set_labels(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    axum_extra::extract::Form(f): axum_extra::extract::Form<LabelsForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (_, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    if role < Role::Triage {
        return Err(Error::not_found(shell));
    }
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    for l in db::issues::labels(&app.db, row.id).await.map_err(|e| Error::from_db(shell.clone(), e))? {
        db::issues::set_proposal_label(&app.db, p.id, l.id, f.label.contains(&l.id)).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    }
    Ok(back(&owner, &name, number, "conversation", None, None))
}

/// `GET /{owner}/{name}/proposal/{number}/events`: server-sent events for
/// checks on the projected state (hub spec §13.1).
pub async fn events(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
) -> Result<axum::response::Sse<impl futures::Stream<Item = Result<axum::response::sse::Event, std::convert::Infallible>>>, Error> {
    use futures::StreamExt;
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let (_, row, _) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let rx = app.events.proposals.subscribe();
    let repo_id = row.id;
    let stream = tokio_stream::wrappers::BroadcastStream::new(rx).filter_map(move |item| async move {
        match item {
            Ok((id, ev)) if id == repo_id => {
                Some(Ok(axum::response::sse::Event::default().event(ev.kind.clone()).data(serde_json::to_string(&ev).unwrap_or_default())))
            }
            _ => None,
        }
    });
    Ok(axum::response::Sse::new(stream).keep_alive(axum::response::sse::KeepAlive::default()))
}

// -------------------------------------------------------------------- API

pub async fn to_api(app: &Shared, owner: &str, name: &str, loaded: &Loaded, v: &Verdict, source_url: Option<String>) -> hub_api::Proposal {
    let p = &loaded.row;
    hub_api::Proposal {
        number: p.number,
        title: p.title.clone(),
        body: p.body.clone(),
        author: p.author.clone(),
        state: ProposalState::parse(&p.state).unwrap_or(ProposalState::Open),
        target: p.target.clone(),
        source: match p.source_kind.as_str() {
            "fork" => {
                let (o, n) = source_url
                    .as_deref()
                    .and_then(|u| u.rsplit_once('/'))
                    .and_then(|(b, n)| b.rsplit_once('/').map(|(_, o)| (o.to_string(), n.to_string())))
                    .unwrap_or_default();
                ProposalSource::Fork { owner: o, name: n, bookmark: p.source_bookmark.clone() }
            }
            "changes" => ProposalSource::Changes { hashes: p.source_changes() },
            _ => ProposalSource::Bookmark { bookmark: p.source_bookmark.clone() },
        },
        changes: loaded
            .changes
            .iter()
            .map(|c| hub_api::ChangeSummary {
                hash: c.hash.clone(),
                message: if c.body.is_empty() { c.title.clone() } else { format!("{}\n\n{}", c.title, c.body) },
                author: hub_api::Author {
                    name: c.author.name.clone(),
                    email: c.author.email.clone(),
                    key: c.author.key.clone(),
                    account: c.author.account.clone(),
                    note: hub_api::Author::note_for(&c.author.key, &c.author.account),
                },
                when_ms: c.when_ms,
                deps: c.deps.clone(),
                head: c.head,
                via: c.via.as_ref().map(|v| hub_api::Via {
                    name: v.name.clone(),
                    key: v.key.clone(),
                    scope: v.scope.clone(),
                    expires_ms: v.expires_ms,
                    revoked: v.revoked,
                }),
                signature: match &c.signature {
                    view::SigView::Unsigned => hub_api::Signature::Unsigned,
                    view::SigView::Valid { key, sealed, revoked, .. } => {
                        hub_api::Signature::Valid { key: key.clone(), sealed: *sealed, revoked: *revoked }
                    }
                    view::SigView::Invalid(why) => hub_api::Signature::Invalid { reason: why.clone() },
                },
            })
            .collect(),
        projected_heads: loaded.heads.iter().map(|h| h.to_hex()).collect(),
        projected_state: Some(loaded.state.clone()),
        conflicted: loaded.conflicted,
        approvals: v.approvals.clone(),
        landable: p.is_open() && v.blockers.is_empty(),
        blockers: v.blockers.clone(),
        created_ms: p.created_ms,
        updated_ms: p.updated_ms,
        url: format!("{}/{owner}/{name}/proposal/{}", app.config.base_url(), p.number),
        repository_url: format!("{}/{owner}/{name}", app.config.base_url()),
        source_url,
        landed: (p.state == "landed" && p.landed_ms > 0).then(|| hub_api::Landed {
            by: p.landed_by.clone(),
            via: p.landed_via.clone(),
            when_ms: p.landed_ms,
        }),
        requested_reviewers: pdb::review_requests(&app.db, p.id).await.unwrap_or_default(),
        labels: db::issues::proposal_labels(&app.db, p.id)
            .await
            .unwrap_or_default()
            .into_iter()
            .map(|l| hub_api::Label { name: l.name, colour: l.colour, description: l.description })
            .collect(),
    }
}

/// The line comment form's placement key, for templates.
pub fn key(path: &str, line: impl filters::Num) -> (String, usize) {
    (path.to_string(), line.as_u64() as usize)
}

#[allow(dead_code)]
fn _unused(_: &diff::Line, _: &ConflictView, _: &Role) {}

// ------------------------------------------------------- review requests

/// Ask accounts to review a proposal (hub plan 0.4): each must exist, be
/// someone other than the author, and be able to read the repository. Each
/// newly asked is told, and the proposal records it. The usernames newly
/// asked, or why none could be.
pub async fn request_reviewers(
    app: &Shared,
    row: &db::repos::RepoRow,
    p: &pdb::ProposalRow,
    by: &accounts::Account,
    names: &[String],
) -> Result<Vec<String>, String> {
    let mut found = Vec::new();
    for name in names.iter().map(|n| n.trim().trim_start_matches('@')).filter(|n| !n.is_empty()) {
        let Some(a) = accounts::account_by_name(&app.db, name).await.ok().flatten() else {
            return Err(format!("There is no account {name}."));
        };
        if Some(a.id) == p.author_id {
            return Err(format!("{name} wrote this proposal, and cannot review it."));
        }
        let role = crate::auth::roles::role_for(&app.db, Some(&a), row).await.ok().flatten();
        if !crate::auth::roles::allows(role, crate::auth::Access::Read) {
            return Err(format!("{name} cannot read this repository."));
        }
        found.push(a);
    }
    let mut asked = Vec::new();
    for a in found {
        if !pdb::request_review(&app.db, p.id, a.id, &by.username).await.map_err(|e| e.to_string())? {
            continue;
        }
        pdb::add_event(&app.db, p.id, &by.username, "review requested", &a.username).await.ok();
        crate::notify::deliver(
            app,
            crate::notify::Event {
                kind: "proposal.review_requested",
                title: format!("{}/{}#{}: {} (review requested from {})", row.owner, row.name, p.number, p.title, a.username),
                url: format!("/{}/{}/proposal/{}", row.owner, row.name, p.number),
                actor: by,
                repo_id: row.id,
                thread: None,
                mention_text: "",
                direct: vec![a.id],
            },
        )
        .await;
        asked.push(a.username);
    }
    Ok(asked)
}

/// After a review: it answers the reviewer's request, if there was one, and
/// the proposal's author is told.
pub async fn reviewed(app: &Shared, row: &db::repos::RepoRow, p: &pdb::ProposalRow, by: &accounts::Account, verdict: &str) {
    pdb::unrequest_review(&app.db, p.id, by.id).await.ok();
    let what = match verdict {
        "approve" => "approved",
        "changes" => "changes requested",
        _ => "reviewed",
    };
    crate::notify::deliver(
        app,
        crate::notify::Event {
            kind: "proposal.review",
            title: format!("{}/{}#{}: {} ({what} by {})", row.owner, row.name, p.number, p.title, by.username),
            url: format!("/{}/{}/proposal/{}", row.owner, row.name, p.number),
            actor: by,
            repo_id: row.id,
            thread: Some(("proposal", p.id)),
            mention_text: "",
            direct: p.author_id.into_iter().collect(),
        },
    )
    .await;
}

#[derive(Deserialize)]
pub struct ReviewersForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    /// `add`, `remove`, or `set` (the menu: exactly these are asked).
    action: String,
    #[serde(default)]
    username: Vec<String>,
}

/// `POST /{owner}/{name}/proposal/{number}/reviewers`: the author or a
/// writer asks someone to review, or withdraws the request.
pub async fn reviewers(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    axum_extra::extract::Form(f): axum_extra::extract::Form<ReviewersForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (_, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if Some(me.account.id) != p.author_id && role < Role::Write {
        return Err(Error::not_found(shell));
    }
    let names: Vec<String> = f.username.iter().map(|n| n.trim().trim_start_matches('@').to_string()).filter(|n| !n.is_empty()).collect();
    let current = pdb::review_requests(&app.db, p.id).await.map_err(|e| Error::from_db(shell.clone(), e))?;
    // Withdrawn: those named (remove), or those the menu left out (set).
    let withdraw: Vec<String> = match f.action.as_str() {
        "remove" => names.clone(),
        "set" => current.iter().filter(|c| !names.iter().any(|n| n.eq_ignore_ascii_case(c))).cloned().collect(),
        _ => Vec::new(),
    };
    for who in &withdraw {
        if let Some(a) = accounts::account_by_name(&app.db, who).await.ok().flatten() {
            if pdb::unrequest_review(&app.db, p.id, a.id).await.map_err(|e| Error::from_db(shell.clone(), e))? {
                pdb::add_event(&app.db, p.id, &me.account.username, "review request withdrawn", &a.username).await.ok();
            }
        }
    }
    let ask: Vec<String> = match f.action.as_str() {
        "add" => names,
        "set" => names.into_iter().filter(|n| !current.iter().any(|c| c.eq_ignore_ascii_case(n))).collect(),
        _ => return Ok(back(&owner, &name, number, "conversation", None, None)),
    };
    if ask.is_empty() {
        return Ok(back(&owner, &name, number, "conversation", None, None));
    }
    match request_reviewers(&app, &row, &p, &me.account, &ask).await {
        Ok(asked) if asked.is_empty() => Ok(back(&owner, &name, number, "conversation", Some("Already asked.".into()), None)),
        Ok(asked) => Ok(back(&owner, &name, number, "conversation", Some(format!("Asked {} to review.", asked.join(", "))), None)),
        Err(e) => Ok(back(&owner, &name, number, "conversation", None, Some(e))),
    }
}

#[derive(Deserialize)]
pub struct AssistantForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    assistant: String,
    /// `summary` asks for a summary comment (oxygenhub#190); otherwise a review.
    #[serde(default)]
    task: String,
}

/// `POST /{owner}/{name}/proposal/{number}/assistant`: the author or a
/// writer asks an AI assistant to review (hub spec §13.4). The answer
/// comes later as a review via the assistant.
pub async fn assistant(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<AssistantForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (_, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if Some(me.account.id) != p.author_id && role < Role::Write {
        return Err(Error::not_found(shell));
    }
    if !p.is_open() {
        return Ok(back(&owner, &name, number, "conversation", None, Some("The proposal is not open.".into())));
    }
    let Some(a) = crate::assistants::enabled_for_repo(&app.db, &row)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .into_iter()
        .find(|a| a.name.eq_ignore_ascii_case(f.assistant.trim()))
    else {
        return Ok(back(&owner, &name, number, "conversation", None, Some(format!("No assistant called {} here.", f.assistant.trim()))));
    };
    let who = a.name.clone();
    let summary = f.task == "summary";
    let asked = if summary {
        crate::assistants::request_summary(&app, &row, &p, &me.account, a).await
    } else {
        crate::assistants::request_review(&app, &row, &p, &me.account, a).await
    };
    match asked {
        Ok(()) => Ok(back(
            &owner,
            &name,
            number,
            "conversation",
            Some(if summary {
                format!("Asked {who} for a summary; its comment appears here when it comes.")
            } else {
                format!("Asked {who} to review; its answer appears here when it comes.")
            }),
            None,
        )),
        Err(e) => Ok(back(&owner, &name, number, "conversation", None, Some(format!("Not asked: {e}.")))),
    }
}

/// The assistants a repository may use, by name.
async fn assistant_names(app: &Shared, row: &db::repos::RepoRow) -> Vec<String> {
    crate::assistants::enabled_for_repo(&app.db, row).await.unwrap_or_default().into_iter().map(|a| a.name).collect()
}

/// The changes and the file diffs a proposal from `source` into `target`
/// would carry.
async fn preview_diff(
    app: &Shared,
    repo: &RepoName,
    target: &str,
    source: &str,
) -> Result<(Vec<ChangeView>, Vec<oxy_core::repo::FileDiff>), crate::repos::RepoError> {
    let Some((fork, bookmark)) = parse_source(app, repo, source) else { return Ok((vec![], vec![])) };
    let target = target.to_string();
    let fork_dir = fork.as_ref().map(|f| app.repos.dir(f));
    app.repos
        .read(repo, move |r, cache| {
            let projection = match &fork_dir {
                Some(dir) => {
                    let fork_repo = oxy_core::repo::Repo::open(dir)?;
                    let heads = fork_repo.bookmarks()?.into_iter().find(|b| b.name == bookmark).map(|b| b.heads).unwrap_or_default();
                    pl::project(r, cache, &target, Source::Fork { fork: &fork_repo, heads })?
                }
                None => {
                    let heads = r.bookmarks()?.into_iter().find(|b| b.name == bookmark).map(|b| b.heads).unwrap_or_default();
                    pl::project(r, cache, &target, Source::Bookmark(heads))?
                }
            };
            Ok((projection.changes, projection.files))
        })
        .await
}

/// `POST /{owner}/{name}/proposals/new/draft`: an assistant drafts the
/// description from the changes the proposal would add; the form comes
/// back with the draft to edit (hub spec §13.4).
pub async fn new_draft(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name)): Path<(String, String)>,
    Form(f): Form<NewForm>,
) -> Result<Page<NewProposalPage>, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposals/new"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (repo, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let bookmarks =
        app.repos.read(&repo, |r, _| Ok(r.bookmarks()?.into_iter().map(|b| b.name).collect::<Vec<_>>())).await.unwrap_or_default();
    let (preview, conflicted) = preview_for(&app, &repo, &f.target, &f.source).await.unwrap_or((vec![], false));
    let assistants = if preview.is_empty() { vec![] } else { assistant_names(&app, &row).await };
    let mut page = NewProposalPage {
        shell,
        repo: RepoShell::new(&app, &row, "proposals").with_role(role),
        bookmarks,
        source: f.source.clone(),
        target: f.target.clone(),
        error: None,
        preview,
        conflicted,
        title: f.title.clone(),
        body: f.body.clone(),
        assistants,
    };
    let assistant = crate::assistants::enabled_for_repo(&app.db, &row)
        .await
        .unwrap_or_default()
        .into_iter()
        .find(|a| a.name.eq_ignore_ascii_case(f.assistant.trim()));
    let Some(a) = assistant else {
        page.error = Some(format!("No assistant called {} here.", f.assistant.trim()));
        return Ok(Page(page));
    };
    if page.preview.is_empty() {
        page.error = Some("Nothing to describe: the source adds nothing to the target.".into());
        return Ok(Page(page));
    }
    let (changes, diffs) = match preview_diff(&app, &repo, &f.target, &f.source).await {
        Ok(x) => x,
        Err(e) => {
            page.error = Some(e.to_string());
            return Ok(Page(page));
        }
    };
    let d = crate::assistants::Draft { slot: -row.id, title: &f.title, target: &f.target, changes: &changes, diffs: &diffs };
    match crate::assistants::draft_description(&app, &row, &me.account, &a, d).await {
        Ok(text) => page.body = text,
        Err(why) => page.error = Some(format!("{} did not answer: {why}.", a.name)),
    }
    Ok(Page(page))
}

#[derive(Deserialize)]
pub struct DraftForm {
    #[serde(rename = "_csrf")]
    csrf_token: String,
    assistant: String,
    #[serde(default)]
    title: String,
}

/// `POST /{owner}/{name}/proposal/{number}/draft`: an assistant drafts the
/// description of an open proposal from its changes; the editor opens
/// with the draft, nothing is saved (hub spec §13.4).
pub async fn draft(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<DraftForm>,
) -> Result<Response, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (repo, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if Some(me.account.id) != p.author_id && role < Role::Maintain {
        return Err(Error::not_found(shell));
    }
    let Some(a) = crate::assistants::enabled_for_repo(&app.db, &row)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .into_iter()
        .find(|a| a.name.eq_ignore_ascii_case(f.assistant.trim()))
    else {
        return Ok(back(&owner, &name, number, "conversation", None, Some(format!("No assistant called {} here.", f.assistant.trim()))));
    };
    let loaded = crate::web::proposals::load(&app, &repo, p.clone()).await.map_err(|e| Error::from_repo(shell.clone(), e))?;
    let title = if f.title.trim().is_empty() { p.title.clone() } else { f.title.clone() };
    let d = crate::assistants::Draft { slot: p.id, title: &title, target: &p.target, changes: &loaded.changes, diffs: &loaded.diffs };
    let draft = crate::assistants::draft_description(&app, &row, &me.account, &a, d).await;
    match draft {
        Ok(text) => {
            let mut page = detail(&app, shell, &viewer, &owner, &name, number, "conversation".into(), None, None).await?;
            page.0.draft = Some(text);
            Ok(page.into_response())
        }
        Err(why) => Ok(back(&owner, &name, number, "conversation", None, Some(format!("{} did not answer: {why}.", a.name)))),
    }
}

/// A draft being written, as server-sent events for the page: `part` with
/// each piece of text, then `done` with the whole draft or `error` with
/// why there is none (each a JSON string). The response starts at once, so
/// a draft that takes minutes is not cut off by a proxy waiting for it
/// (oxygenhub#248).
type DraftEvents = axum::response::Sse<
    axum::response::sse::KeepAliveStream<
        tokio_stream::wrappers::ReceiverStream<Result<axum::response::sse::Event, std::convert::Infallible>>,
    >,
>;

fn draft_events(rx: tokio::sync::mpsc::Receiver<Result<axum::response::sse::Event, std::convert::Infallible>>) -> DraftEvents {
    axum::response::Sse::new(tokio_stream::wrappers::ReceiverStream::new(rx))
        .keep_alive(axum::response::sse::KeepAlive::new().interval(std::time::Duration::from_secs(15)))
}

fn draft_event(kind: &str, text: &str) -> Result<axum::response::sse::Event, std::convert::Infallible> {
    Ok(axum::response::sse::Event::default().event(kind).data(serde_json::to_string(text).unwrap_or_default()))
}

/// Only an error, for a draft that cannot start.
fn draft_refused(why: String) -> DraftEvents {
    let (tx, rx) = tokio::sync::mpsc::channel(1);
    let _ = tx.try_send(draft_event("error", &why));
    draft_events(rx)
}

/// What a draft is written from, owned so a task of its own can have it.
struct DraftJob {
    row: db::repos::RepoRow,
    by: accounts::Account,
    a: crate::assistants::Assistant,
    slot: i64,
    title: String,
    target: String,
    changes: Vec<ChangeView>,
    diffs: Vec<oxy_core::repo::FileDiff>,
}

/// Write the draft in a task of its own, its parts to the page.
fn draft_in_background(app: Shared, job: DraftJob) -> DraftEvents {
    let (tx, rx) = tokio::sync::mpsc::channel(64);
    tokio::spawn(async move {
        let DraftJob { row, by, a, slot, title, target, changes, diffs } = job;
        let d = crate::assistants::Draft { slot, title: &title, target: &target, changes: &changes, diffs: &diffs };
        let parts = tx.clone();
        let result = crate::assistants::draft_description_streaming(&app, &row, &by, &a, d, move |p: &str| {
            // A page that went away stops nothing: the draft finishes.
            let _ = parts.try_send(draft_event("part", p));
        })
        .await;
        let last = match result {
            Ok(text) => draft_event("done", text.trim()),
            Err(why) => draft_event("error", &format!("{} did not answer: {why}.", a.name)),
        };
        let _ = tx.send(last).await;
    });
    draft_events(rx)
}

/// `POST /{owner}/{name}/proposal/{number}/draft/stream`: [`draft`], with
/// the draft streamed to the page as it is written.
pub async fn draft_stream(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name, number)): Path<(String, String, i64)>,
    Form(f): Form<DraftForm>,
) -> Result<DraftEvents, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposal/{number}"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (repo, row, role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let p = pdb::get(&app.db, row.id, number)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .ok_or_else(|| Error::not_found(shell.clone()))?;
    if Some(me.account.id) != p.author_id && role < Role::Maintain {
        return Err(Error::not_found(shell));
    }
    let Some(a) = crate::assistants::enabled_for_repo(&app.db, &row)
        .await
        .map_err(|e| Error::from_db(shell.clone(), e))?
        .into_iter()
        .find(|a| a.name.eq_ignore_ascii_case(f.assistant.trim()))
    else {
        return Ok(draft_refused(format!("No assistant called {} here.", f.assistant.trim())));
    };
    let loaded = load(&app, &repo, p.clone()).await.map_err(|e| Error::from_repo(shell.clone(), e))?;
    let title = if f.title.trim().is_empty() { p.title.clone() } else { f.title.clone() };
    let job = DraftJob {
        row,
        by: me.account.clone(),
        a,
        slot: p.id,
        title,
        target: p.target.clone(),
        changes: loaded.changes,
        diffs: loaded.diffs,
    };
    Ok(draft_in_background(app.clone(), job))
}

/// `POST /{owner}/{name}/proposals/new/draft/stream`: [`new_draft`], with
/// the draft streamed to the page as it is written.
pub async fn new_draft_stream(
    State(app): State<Shared>,
    viewer: Viewer,
    Path((owner, name)): Path<(String, String)>,
    Form(f): Form<NewForm>,
) -> Result<DraftEvents, Error> {
    let shell = Shell::new(&app, &format!("/{owner}/{name}/proposals/new"), &viewer);
    let me = require(&viewer, &shell)?;
    csrf(&viewer, &f.csrf_token, &shell)?;
    let (repo, row, _role) = lookup(&app, &shell, &viewer, &owner, &name).await?;
    super::writable(&row, &shell)?;
    let Some(a) = crate::assistants::enabled_for_repo(&app.db, &row)
        .await
        .unwrap_or_default()
        .into_iter()
        .find(|a| a.name.eq_ignore_ascii_case(f.assistant.trim()))
    else {
        return Ok(draft_refused(format!("No assistant called {} here.", f.assistant.trim())));
    };
    let (changes, diffs) = match preview_diff(&app, &repo, &f.target, &f.source).await {
        Ok(x) => x,
        Err(e) => return Ok(draft_refused(e.to_string())),
    };
    if changes.is_empty() {
        return Ok(draft_refused("Nothing to describe: the source adds nothing to the target.".into()));
    }
    let job = DraftJob { slot: -row.id, row, by: me.account.clone(), a, title: f.title.clone(), target: f.target.clone(), changes, diffs };
    Ok(draft_in_background(app.clone(), job))
}
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