travelagent-core 1.10.0

//! Pure re-anchoring pipeline for the live-review rescan loop.
//!
//! When the working tree changes underneath an open review session, the
//! diff's "new side" line numbers shift. [`reanchor_comments`] walks every
//! file in a [`ReviewSession`], builds an [`AnchorMap`] between the
//! pre-rescan "new side" snapshot and the post-rescan content, and re-keys
//! each file's `line_comments` map accordingly. Comments whose line
//! disappeared are moved to `orphaned_comments` with their last-seen
//! content preserved so the user can surface / re-anchor them later.
//!
//! # Why this lives in `core`
//!
//! The function is pure: no I/O, no TUI state, no `App`. Callers are
//! responsible for reading file content from disk (or wherever) and passing
//! it in via `new_content_map`. Keeping the pure core here lets the TUI,
//! MCP server, and future headless `ReviewEngine` share the same anchor
//! semantics without each re-implementing them.
//!
//! # Missing-content policy
//!
//! When a tracked path is absent from `new_content_map` the caller's
//! preload failed (or the file vanished from disk); we treat those cases
//! differently:
//!
//! * If `path_filter_active` is set, filtered-out files are left alone —
//!   the file may still exist on disk, we just aren't showing it.
//! * If the path is in `new_paths` (the rescan saw it) but missing from
//!   `new_content_map`, the preload returned `Err`. Skip re-anchoring for
//!   this file — preserve existing anchor state rather than silently
//!   orphaning every comment. Callers should log the error (pending
//!   `ErrorLog` from H8).
//! * If the path is NOT in `new_paths` at all, the file truly disappeared;
//!   orphan its comments (preserving the pre-H4 behavior).

use std::collections::{HashMap, HashSet};
use std::path::{Path, PathBuf};

use crate::anchor_map::AnchorMap;
use crate::model::review::{FileReview, ReviewSession};
use crate::model::{AnchorState, Comment, DiffFile, FileStatus, LineSide};

/// Remap `old_new_content` keys in-place: for every `FileStatus::Renamed`
/// entry in `diff_files`, move the snapshot at `old_path` to `new_path`.
/// Caller must invoke this BEFORE running [`reanchor_comments`] on a
/// session that has already absorbed the same `diff_files` via
/// `apply_diff_files` — the session now keys files by the new path, so
/// the pre-rescan snapshot must be rekeyed too or every line comment on
/// a renamed file silently orphans (H6.11).
///
/// Safe to call with an unchanged `diff_files` — non-`Renamed` entries
/// and renames whose old path isn't in the map are ignored.
///
/// **Collision-safe two-pass implementation.** A naive single-pass insert
/// would clobber an existing `new_path` snapshot: imagine a diff with
/// rename `A→B` where `B` was also in the pre-rescan snapshot (because it
/// was separately touched). `insert(B, A_content)` would drop B's own
/// pre-rescan content, and subsequent re-anchoring of comments already
/// living on B would run against A's text — wrong line mappings. We
/// instead stage sources first (via `remove`), then insert, skipping
/// destinations that still hold a distinct snapshot. This also means A↔B
/// swaps are handled correctly: pass 1 removes both A and B, pass 2
/// re-inserts them at their new keys.
///
/// **Transitive rename chains.** For a diff containing both `A→B` and
/// `B→C` (rare outside aggregated forge diffs), we resolve each source
/// to its terminal destination via [`resolve_terminal_dest`] before
/// staging. So A's snapshot lands at C, B's also at C — the final
/// `.or_insert` keeps whichever settles first; the other is dropped
/// because both describe the pre-rescan content of paths that no
/// longer exist post-rescan.
///
/// **Collision policy — intentional divergence from `apply_diff_files`.**
/// On a pass-2 collision (rename `A→B` where `B` already has a snapshot),
/// this function keeps the destination's snapshot via `.or_insert` and
/// drops the source's. The sibling policy on `FileReview` state, in
/// [`ReviewSession::apply_diff_files`], instead *merges* via
/// [`FileReview::absorb_rename_source`] — which orphans source line
/// comments rather than remapping them. The two decisions are coupled:
/// because we keep the destination's *content*, source line comments
/// would re-anchor against the wrong text, so `absorb_rename_source`
/// orphans them instead. Keep both policies in sync if either changes.
pub fn remap_rename_keys(old_new_content: &mut HashMap<PathBuf, String>, diff_files: &[DiffFile]) {
    let direct = direct_rename_map(diff_files);

    // Pass 1: extract every rename source out of the map, keyed by
    // terminal destination (not direct destination) so transitive
    // chains `A→B, B→C` land A and B both at C.
    let mut staged: Vec<(PathBuf, String)> = Vec::new();
    for src in direct.keys() {
        if let Some(content) = old_new_content.remove(src) {
            let dst = resolve_terminal_dest(src, &direct);
            staged.push((dst, content));
        }
    }

    // Pass 2: settle staged entries. If a destination still holds a
    // snapshot (i.e. it was not itself a rename source and happened to be
    // touched independently in the same rescan), leave it alone — the
    // destination's own comments re-anchor against its own content, and
    // the renamed-source content would produce wrong mappings.
    for (new_path, content) in staged {
        old_new_content.entry(new_path).or_insert(content);
    }
}

/// Build a `src → dst` map from every `FileStatus::Renamed` entry where
/// the paths differ. Used by chain resolution.
pub(crate) fn direct_rename_map(diff_files: &[DiffFile]) -> HashMap<PathBuf, PathBuf> {
    let mut map = HashMap::new();
    for file in diff_files {
        if file.status == FileStatus::Renamed
            && let (Some(old), Some(new)) = (file.old_path.as_ref(), file.new_path.as_ref())
            && old.as_path() != new.as_path()
        {
            map.insert(old.clone(), new.clone());
        }
    }
    map
}

/// Walk the rename chain starting at `src` and return the terminal
/// destination — the last path that is not itself a rename source in
/// `direct`, OR (on cycle) the last fresh hop before the cycle closes.
///
/// For a two-path swap `A→B, B→A`, resolving from A walks A→B, sees
/// B→A would revisit A, stops and returns B. From B it returns A. So
/// the swap round-trips both paths to each other, matching the
/// established swap semantics.
pub(crate) fn resolve_terminal_dest(src: &Path, direct: &HashMap<PathBuf, PathBuf>) -> PathBuf {
    let mut current = src.to_path_buf();
    let mut visited: HashSet<PathBuf> = HashSet::new();
    visited.insert(current.clone());
    while let Some(next) = direct.get(&current) {
        if visited.contains(next) {
            // The next hop would revisit a path we've already walked
            // through (a cycle — usually a swap). Don't follow it;
            // `current` is the terminal for this branch of the cycle.
            return current;
        }
        visited.insert(next.clone());
        current = next.clone();
    }
    current
}

/// Look up the post-rescan path for a pre-rescan path. Returns `Some(new)`
/// when `path` appears as `old_path` on a `FileStatus::Renamed` entry in
/// `diff_files`, else `None`. Callers that forward a cursor or lookup
/// path through a rename use this instead of mutating a map.
///
/// Chain-aware: if a diff contains `A→B, B→C`, `remap_path(A, diff)` walks
/// through to the terminal destination `C` (not the intermediate `B`),
/// so a cursor on `A` lands on the same terminal the session-state and
/// content-snapshot migration landed on. Matches the policy in
/// [`ReviewSession::apply_diff_files`] and [`remap_rename_keys`].
pub fn remap_path(path: &Path, diff_files: &[DiffFile]) -> Option<PathBuf> {
    let direct = direct_rename_map(diff_files);
    if !direct.contains_key(path) {
        return None;
    }
    Some(resolve_terminal_dest(path, &direct))
}

/// Pure core of the L2 comment-survival pipeline. Walks every file in
/// `session.files`, builds an [`AnchorMap`] between the pre-rescan "new
/// side" snapshot (`old_new_content`) and the post-rescan content
/// (`new_content_map`), and re-keys the `line_comments` map accordingly.
/// Comments whose line disappeared move to `orphaned_comments` with their
/// last-seen content preserved.
///
/// No I/O. See the module-level docs for the missing-content policy when a
/// path is absent from `new_content_map`.
pub fn reanchor_comments(
    session: &mut ReviewSession,
    old_new_content: &HashMap<PathBuf, String>,
    new_content_map: &HashMap<PathBuf, String>,
    new_paths: &HashSet<PathBuf>,
    path_filter_active: bool,
) {
    for (path, review) in session.files.iter_mut() {
        // Legacy: side-only comments with no explicit anchor get stamped
        // with `Anchored { line, side }` for their current HashMap key on
        // first touch. We do this so subsequent rescans have a concrete
        // anchor state to roll forward.
        stamp_anchors_from_keys(review);

        if review.line_comments.is_empty() {
            continue;
        }

        // File disappeared entirely: orphan every comment. But if
        // `path_filter` is active the file may just be hidden — we can't
        // tell disappeared-from-disk apart from filtered-out here, so
        // leave filtered files untouched.
        if !new_paths.contains(path) {
            if path_filter_active {
                continue;
            }
            let old_content = old_new_content.get(path).cloned().unwrap_or_default();
            let old_lines: Vec<&str> = old_content.lines().collect();
            let line_comments: HashMap<u32, Vec<Comment>> =
                std::mem::take(&mut review.line_comments);
            for (line, comments) in line_comments {
                for comment in comments {
                    let side = comment_side(&comment, line);
                    // `old_content` is the pre-rescan NEW-side snapshot, so
                    // indexing it by a `LineSide::Old` comment's base-commit
                    // line number returns unrelated new-side text and
                    // confuses the orphaned-section UI. Skip the lookup for
                    // old-side orphans — the UI already handles an empty
                    // `last_seen_content`.
                    let last_seen = if side == LineSide::Old {
                        String::new()
                    } else {
                        old_lines
                            .get((line as usize).saturating_sub(1))
                            .map(|s| s.to_string())
                            .unwrap_or_default()
                    };
                    review.orphan_comment(line, side, last_seen, comment);
                }
            }
            continue;
        }

        // Path is tracked by the rescan but the preload couldn't read
        // it. Preserve existing anchors — do NOT orphan, do NOT silently
        // treat as empty. The previous implementation here read the
        // file with `unwrap_or_default()`, which degenerated to an
        // `AnchorMap::from_content("", "")` (identity) or `("", non-empty)`
        // (no mapping) and either silently skipped or orphaned every
        // comment depending on whether `old_content` was also empty.
        let Some(new_content) = new_content_map.get(path) else {
            continue;
        };

        let old_content = old_new_content.get(path).cloned().unwrap_or_default();
        let anchor_map = AnchorMap::from_content(&old_content, new_content);

        // Short-circuit if nothing moved. Legacy comments that lacked an
        // explicit anchor were just stamped above, so this branch is safe
        // to return to without re-anchoring.
        if anchor_map.is_identity() {
            continue;
        }

        let old_lines: Vec<&str> = old_content.lines().collect();
        let original: HashMap<u32, Vec<Comment>> = std::mem::take(&mut review.line_comments);
        let mut next: HashMap<u32, Vec<Comment>> = HashMap::new();

        for (line, comments) in original {
            for mut comment in comments {
                let side = comment_side(&comment, line);
                // The AnchorMap only covers the new side. Deletion-side
                // comments (`LineSide::Old`) reference lines that no
                // longer exist in the new-side content, so a new-side
                // lookup would be meaningless. Preserve the old-side key
                // as-is; if the file was re-added later and the old line
                // was restored, subsequent rescans can still reconcile.
                if side == LineSide::Old {
                    next.entry(line).or_default().push(comment);
                    continue;
                }
                match anchor_map.lookup(line) {
                    Some(new_line) => {
                        // Preserve any existing `reanchored_at` stamp
                        // — the comment was already anchored before
                        // this rescan, we're just shifting its line
                        // number, not re-anchoring from an orphan.
                        let reanchored_at = match comment.anchor.as_ref() {
                            Some(AnchorState::Anchored { reanchored_at, .. }) => *reanchored_at,
                            _ => None,
                        };
                        comment.anchor = Some(AnchorState::Anchored {
                            line: new_line,
                            side,
                            reanchored_at,
                        });
                        next.entry(new_line).or_default().push(comment);
                    }
                    None => {
                        let last_seen = old_lines
                            .get((line as usize).saturating_sub(1))
                            .map(|s| s.to_string())
                            .unwrap_or_default();
                        review.orphan_comment(line, side, last_seen, comment);
                    }
                }
            }
        }
        review.line_comments = next;
    }
}

/// Resolve the side a comment lives on. Falls back to `New` when the
/// comment's `side` field is absent (legacy) — the HashMap key is the
/// line number; for deletion comments the map uses the old line and
/// `side = Old`, but a missing field defaults to `New`, matching the
/// shape `Comment::new` would have produced.
fn comment_side(comment: &Comment, _fallback_line: u32) -> LineSide {
    comment.side.unwrap_or(LineSide::New)
}

/// Stamp `Anchored { line, side }` onto every comment that still has
/// `anchor == None`. Idempotent — comments that already carry an anchor
/// are left alone. Run on first rescan so subsequent passes can treat
/// `anchor` as authoritative.
fn stamp_anchors_from_keys(review: &mut FileReview) {
    for (line, comments) in review.line_comments.iter_mut() {
        for comment in comments.iter_mut() {
            if comment.anchor.is_none() {
                let side = comment.side.unwrap_or(LineSide::New);
                comment.anchor = Some(AnchorState::Anchored {
                    line: *line,
                    side,
                    reanchored_at: None,
                });
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::model::comment::CommentType;
    use crate::model::{DiffFile, FileStatus};

    fn df_renamed(old: &str, new: &str) -> DiffFile {
        DiffFile {
            old_path: Some(PathBuf::from(old)),
            new_path: Some(PathBuf::from(new)),
            status: FileStatus::Renamed,
            hunks: vec![],
            is_binary: false,
            is_too_large: false,
            is_commit_message: false,
        }
    }

    fn df_modified(path: &str) -> DiffFile {
        DiffFile {
            old_path: Some(PathBuf::from(path)),
            new_path: Some(PathBuf::from(path)),
            status: FileStatus::Modified,
            hunks: vec![],
            is_binary: false,
            is_too_large: false,
            is_commit_message: false,
        }
    }

    #[test]
    fn remap_rename_keys_moves_snapshot_to_new_path() {
        let mut map: HashMap<PathBuf, String> = HashMap::new();
        map.insert(PathBuf::from("old.rs"), "hello\n".into());
        map.insert(PathBuf::from("unchanged.rs"), "other\n".into());

        remap_rename_keys(&mut map, &[df_renamed("old.rs", "new.rs")]);

        assert!(!map.contains_key(Path::new("old.rs")));
        assert_eq!(
            map.get(Path::new("new.rs")).map(String::as_str),
            Some("hello\n")
        );
        assert_eq!(
            map.get(Path::new("unchanged.rs")).map(String::as_str),
            Some("other\n"),
            "non-renamed entries are left alone"
        );
    }

    #[test]
    fn remap_rename_keys_ignores_non_renamed() {
        let mut map: HashMap<PathBuf, String> = HashMap::new();
        map.insert(PathBuf::from("a.rs"), "x\n".into());
        remap_rename_keys(&mut map, &[df_modified("a.rs")]);
        assert_eq!(map.get(Path::new("a.rs")).map(String::as_str), Some("x\n"));
    }

    #[test]
    fn remap_rename_keys_preserves_destination_snapshot_on_collision() {
        // Regression: a diff containing `A→B` where `B` already has its own
        // pre-rescan snapshot (because B was also touched) must not clobber
        // B's snapshot with A's content. B's own comments re-anchor against
        // B's own content; A's renamed-over content would produce wrong
        // line mappings.
        let mut map: HashMap<PathBuf, String> = HashMap::new();
        map.insert(PathBuf::from("a.rs"), "a-content\n".into());
        map.insert(PathBuf::from("b.rs"), "b-content\n".into());

        remap_rename_keys(&mut map, &[df_renamed("a.rs", "b.rs")]);

        assert!(
            !map.contains_key(Path::new("a.rs")),
            "source entry removed even on collision"
        );
        assert_eq!(
            map.get(Path::new("b.rs")).map(String::as_str),
            Some("b-content\n"),
            "destination's own snapshot is preserved"
        );
    }

    #[test]
    fn remap_rename_keys_swaps_two_paths_without_loss() {
        // Regression: a diff containing `A→B` AND `B→A` (a swap) must end
        // with A holding B's old content and B holding A's old content.
        // Single-pass insert would let the second rename overwrite the
        // first.
        let mut map: HashMap<PathBuf, String> = HashMap::new();
        map.insert(PathBuf::from("a.rs"), "a-content\n".into());
        map.insert(PathBuf::from("b.rs"), "b-content\n".into());

        remap_rename_keys(
            &mut map,
            &[df_renamed("a.rs", "b.rs"), df_renamed("b.rs", "a.rs")],
        );

        assert_eq!(
            map.get(Path::new("a.rs")).map(String::as_str),
            Some("b-content\n"),
            "a.rs now holds b's original content"
        );
        assert_eq!(
            map.get(Path::new("b.rs")).map(String::as_str),
            Some("a-content\n"),
            "b.rs now holds a's original content"
        );
    }

    #[test]
    fn remap_rename_keys_resolves_transitive_rename_chain() {
        // Regression (H6.19): a diff containing both `A→B` and `B→C`
        // must land A's snapshot at the terminal destination C. The
        // pre-H6.19 single-hop implementation staged A at B (which is
        // itself a rename source with no destination in `self.files`
        // post-extraction), so A's content was lost even though C had
        // no existing snapshot to preserve.
        let mut map: HashMap<PathBuf, String> = HashMap::new();
        map.insert(PathBuf::from("a.rs"), "a-content\n".into());
        map.insert(PathBuf::from("b.rs"), "b-content\n".into());

        remap_rename_keys(
            &mut map,
            &[df_renamed("a.rs", "b.rs"), df_renamed("b.rs", "c.rs")],
        );

        assert!(!map.contains_key(Path::new("a.rs")), "a consumed");
        assert!(
            !map.contains_key(Path::new("b.rs")),
            "b consumed as intermediate"
        );
        // Both A's and B's pre-rescan snapshots land at C. `.or_insert`
        // keeps whichever settles first; the other is dropped because
        // both describe content at paths that no longer exist.
        let at_c = map.get(Path::new("c.rs")).expect("c is terminal");
        assert!(
            at_c == "a-content\n" || at_c == "b-content\n",
            "c holds one of the chain-collapsed snapshots, got {at_c:?}"
        );
    }

    #[test]
    fn remap_rename_keys_skips_missing_snapshot() {
        let mut map: HashMap<PathBuf, String> = HashMap::new();
        map.insert(PathBuf::from("untouched.rs"), "z\n".into());
        remap_rename_keys(&mut map, &[df_renamed("missing.rs", "also-missing.rs")]);
        assert!(map.contains_key(Path::new("untouched.rs")));
        assert!(!map.contains_key(Path::new("also-missing.rs")));
    }

    #[test]
    fn remap_path_returns_new_path_for_rename() {
        let diff = [df_renamed("old.rs", "new.rs"), df_modified("other.rs")];
        assert_eq!(
            remap_path(Path::new("old.rs"), &diff).as_deref(),
            Some(Path::new("new.rs"))
        );
        assert_eq!(remap_path(Path::new("other.rs"), &diff), None);
        assert_eq!(remap_path(Path::new("absent.rs"), &diff), None);
    }

    #[test]
    fn remap_path_walks_transitive_rename_chain_to_terminal() {
        // Regression (post-H9 crew review): a cursor on `A` in an
        // `A→B, B→C` diff must land on the terminal destination `C`,
        // matching the landing that `apply_diff_files` and
        // `remap_rename_keys` produce. Before the fix, remap_path only
        // looked up direct `old_path` matches, so the cursor landed on
        // the stale intermediate `B`.
        let diff = [df_renamed("a.rs", "b.rs"), df_renamed("b.rs", "c.rs")];
        assert_eq!(
            remap_path(Path::new("a.rs"), &diff).as_deref(),
            Some(Path::new("c.rs")),
            "A walks through to terminal C, not intermediate B"
        );
        assert_eq!(
            remap_path(Path::new("b.rs"), &diff).as_deref(),
            Some(Path::new("c.rs")),
            "B walks directly to terminal C"
        );
    }

    #[test]
    fn remap_path_breaks_on_swap_cycle() {
        // Companion to `resolve_terminal_dest`'s swap handling: for
        // `A→B, B→A`, remap_path(A) = B and remap_path(B) = A, matching
        // the swap semantics the rest of the pipeline uses.
        let diff = [df_renamed("a.rs", "b.rs"), df_renamed("b.rs", "a.rs")];
        assert_eq!(
            remap_path(Path::new("a.rs"), &diff).as_deref(),
            Some(Path::new("b.rs"))
        );
        assert_eq!(
            remap_path(Path::new("b.rs"), &diff).as_deref(),
            Some(Path::new("a.rs"))
        );
    }

    // Regression test for H6.11: when a file is renamed between rescans
    // AND its content shifts, remap_rename_keys + apply_diff_files +
    // reanchor_comments must follow the content — the comment on "line
    // two" at old-line-2 should end up at new-line-3 after an insertion
    // above it, under the new path, not orphaned and not stuck at line 2.
    #[test]
    fn rename_reanchor_follows_content_through_line_shift() {
        let mut session = ReviewSession::new(
            PathBuf::from("/repo"),
            "abc123".to_string(),
            None,
            crate::model::review::SessionDiffSource::WorkingTree,
        );
        let old_path = PathBuf::from("src/old.rs");
        let new_path = PathBuf::from("src/new.rs");

        let old_content = "line one\nline two\nline three\n";
        let new_content = "inserted\nline one\nline two\nline three\n";

        // Pre-rescan: file at `old_path` with a comment on line 2
        // ("line two").
        session.add_file(old_path.clone(), FileStatus::Modified);
        let file = session.get_file_mut(&old_path).unwrap();
        let mut comment = Comment::new("hi".into(), CommentType::Note, None);
        comment.side = Some(LineSide::New);
        file.add_line_comment(2, comment);

        // `old_new_content` keyed by OLD path, as the TUI builds it from
        // the pre-rescan `self.diff_files`.
        let mut old_new_content: HashMap<PathBuf, String> = HashMap::new();
        old_new_content.insert(old_path.clone(), old_content.into());

        // Rescan reports rename + insertion at top.
        let diff_files = vec![df_renamed("src/old.rs", "src/new.rs")];

        // Apply the H6.11 fix: remap keys BEFORE apply_diff_files migrates
        // session keys, then reanchor.
        remap_rename_keys(&mut old_new_content, &diff_files);
        session.apply_diff_files(&diff_files);

        let mut new_content_map: HashMap<PathBuf, String> = HashMap::new();
        new_content_map.insert(new_path.clone(), new_content.into());
        let mut new_paths: HashSet<PathBuf> = HashSet::new();
        new_paths.insert(new_path.clone());

        reanchor_comments(
            &mut session,
            &old_new_content,
            &new_content_map,
            &new_paths,
            false,
        );

        // Post-rescan: comment moved to line 3 under the new path.
        assert!(!session.files.contains_key(&old_path));
        let migrated = session
            .files
            .get(&new_path)
            .expect("file should live at new path after rename");
        assert!(
            !migrated.line_comments.contains_key(&2),
            "comment should not remain at old line 2"
        );
        assert_eq!(
            migrated.line_comments.get(&3).map(Vec::len),
            Some(1),
            "comment should follow 'line two' to new line 3 after insertion above"
        );
        assert!(
            migrated.orphaned_comments.is_empty(),
            "no comments should be orphaned — content survived, just shifted"
        );
    }

    // Companion regression: without remap_rename_keys, re-anchoring on a
    // rename + line-shift fails to relocate surviving comments — they stay
    // at their stale pre-rescan line number, effectively pointing at the
    // wrong content. The positive test above proves the H6.11 fix moves
    // them correctly; this test proves the fix is load-bearing.
    #[test]
    fn without_remap_rename_keeps_comments_at_stale_line_number() {
        let mut session = ReviewSession::new(
            PathBuf::from("/repo"),
            "abc123".to_string(),
            None,
            crate::model::review::SessionDiffSource::WorkingTree,
        );
        let old_path = PathBuf::from("src/old.rs");
        let new_path = PathBuf::from("src/new.rs");
        let old_content = "line one\nline two\nline three\n";
        let new_content = "inserted\nline one\nline two\nline three\n";

        session.add_file(old_path.clone(), FileStatus::Modified);
        let file = session.get_file_mut(&old_path).unwrap();
        let mut comment = Comment::new("hi".into(), CommentType::Note, None);
        comment.side = Some(LineSide::New);
        file.add_line_comment(2, comment); // anchored on "line two"

        let mut old_new_content: HashMap<PathBuf, String> = HashMap::new();
        old_new_content.insert(old_path.clone(), old_content.into());

        let diff_files = vec![df_renamed("src/old.rs", "src/new.rs")];

        // Intentionally DO NOT call remap_rename_keys — this mimics the
        // pre-H6.11 broken flow.
        session.apply_diff_files(&diff_files);

        let mut new_content_map: HashMap<PathBuf, String> = HashMap::new();
        new_content_map.insert(new_path.clone(), new_content.into());
        let mut new_paths: HashSet<PathBuf> = HashSet::new();
        new_paths.insert(new_path.clone());

        reanchor_comments(
            &mut session,
            &old_new_content,
            &new_content_map,
            &new_paths,
            false,
        );

        // Pre-H6.11 bug: `old_new_content.get("src/new.rs")` misses (key is
        // still "src/old.rs"), falls back to `""`. `AnchorMap::from_content("",
        // new_content)` has an empty mapping, which short-circuits as
        // identity, so `reanchor_comments` skips re-keying. The comment
        // stays on its original line 2 — but line 2 in the NEW content is
        // "line one", not "line two". The comment now anchors the wrong
        // line.
        let migrated = session.files.get(&new_path).expect("rename migrated");
        assert_eq!(
            migrated.line_comments.get(&2).map(Vec::len),
            Some(1),
            "pre-H6.11: comment stuck on stale line number"
        );
        assert!(
            !migrated.line_comments.contains_key(&3),
            "pre-H6.11: comment did NOT move to the correct new line 3"
        );
    }

    // Regression: when a file disappears entirely from the rescan AND a
    // `LineSide::Old` (deletion-side) comment is orphaned, `last_seen_content`
    // must be empty — indexing `old_content` by a base-commit line number
    // returns unrelated new-side text, so we skip the lookup and rely on the
    // UI's empty-last-seen fallback.
    #[test]
    fn file_disappeared_orphan_with_old_side_has_empty_last_seen() {
        use crate::model::AnchorState;
        let mut session = ReviewSession::new(
            PathBuf::from("/repo"),
            "abc123".to_string(),
            None,
            crate::model::review::SessionDiffSource::WorkingTree,
        );
        let path = PathBuf::from("src/gone.rs");
        session.add_file(path.clone(), FileStatus::Modified);
        let file = session.get_file_mut(&path).unwrap();

        // Seed one old-side (deletion) and one new-side comment at the same
        // line number so we can observe both branches of the side switch.
        let mut old_side = Comment::new("old-side".into(), CommentType::Note, None);
        old_side.side = Some(LineSide::Old);
        let mut new_side = Comment::new("new-side".into(), CommentType::Note, None);
        new_side.side = Some(LineSide::New);
        file.add_line_comment(2, old_side);
        file.add_line_comment(2, new_side);

        // `old_new_content` is the pre-rescan NEW-side snapshot.
        let mut old_new_content: HashMap<PathBuf, String> = HashMap::new();
        old_new_content.insert(path.clone(), "keep1\nkeep2\nkeep3\n".into());
        // File disappeared entirely from the rescan.
        let new_paths: HashSet<PathBuf> = HashSet::new();
        let new_content_map: HashMap<PathBuf, String> = HashMap::new();

        reanchor_comments(
            &mut session,
            &old_new_content,
            &new_content_map,
            &new_paths,
            false,
        );

        let review = session.files.get(&path).unwrap();
        assert!(review.line_comments.is_empty(), "all comments orphaned");
        assert_eq!(review.orphaned_comments.len(), 2);

        // Partition orphans by side and check last_seen_content per side.
        let mut saw_old_empty = false;
        let mut saw_new_populated = false;
        for comment in &review.orphaned_comments {
            match comment.anchor.as_ref().unwrap() {
                AnchorState::Orphaned {
                    was_side,
                    last_seen_content,
                    ..
                } => {
                    if *was_side == LineSide::Old {
                        assert!(
                            last_seen_content.is_empty(),
                            "old-side orphan must have empty last_seen_content to avoid \
                             surfacing unrelated new-side text; got {last_seen_content:?}"
                        );
                        saw_old_empty = true;
                    } else {
                        assert_eq!(
                            last_seen_content, "keep2",
                            "new-side orphan pulls last_seen from the pre-rescan snapshot"
                        );
                        saw_new_populated = true;
                    }
                }
                other => panic!("expected Orphaned, got {other:?}"),
            }
        }
        assert!(saw_old_empty, "should see an old-side orphan");
        assert!(saw_new_populated, "should see a new-side orphan");
    }
}