tix-tracker 0.12.0

#[allow(clippy::wildcard_imports)]
use super::*;

impl Store {
    /// Create an issue file atomically and assign its number by scanning the
    /// live issue set (issue #52): the highest existing `number` plus one,
    /// with a floor of `0` for an empty store.
    ///
    /// The number is resolved at creation time rather than read from a
    /// persisted `[state].next_number` counter, so `tix.toml` is never
    /// rewritten by `create`. A deleted high-numbered issue's number can be
    /// reused by a later create; the frontmatter `number` stays stable for
    /// every surviving issue (C-007).
    ///
    /// The file is written into the assignee segment derived from
    /// `issue.assignee` (`unassigned/` fallback, FR-029/FR-030), creating the
    /// segment directory as needed, and `issue.filename` is set to the
    /// relative path so `create` output and later edits agree. Atomic-write
    /// discipline (temp + rename, NFR-006) is preserved.
    pub fn create(
        &self,
        issue: &mut Issue,
        body: &str,
        filename_stem: Option<&str>,
    ) -> Result<PathBuf> {
        issue.body = body.to_string();
        issue.bump_updated();

        std::fs::create_dir_all(&self.issues_dir)?;
        issue.number = self.resolve_next_number()?;

        // Claim the number **before** anything is serialised, and hold it across the
        // whole write. `resolve_next_number` above reads the directory, takes `max`,
        // and adds 1, which is only a *hint*: two processes reaching this line
        // together both get the same answer and both proceed. See [`NumberClaim`]
        // for what that cost and why an `O_EXCL` marker is the fix.
        //
        // **Before** the serialisation, specifically. `to_file_contents` embeds
        // `number:` in the frontmatter, so serialising first and claiming after —
        // which is the order this was first written in — writes a *stale* number into
        // the file while the ledger records the correct one. The 24-create test still
        // saw 8 distinct numbers with 24 valid claims in place, because every claim
        // was correct and every file was wrong. A claim that does not reach the bytes
        // on disk is not a claim.
        let mut claim = NumberClaim::acquire(&self.issues_dir, issue.number)?;
        // Belt and braces (#1352): the number actually claimed must be the number
        // about to be written. `acquire` only climbs when the requested number is
        // already taken, so this is normally an identity — but it means a future
        // change to either side that drifts from the other fails loudly here
        // instead of writing an issue whose `number:` disagrees with the ledger.
        issue.number = claim.number().ok_or_else(|| {
            TixError::Io(std::io::Error::new(
                std::io::ErrorKind::InvalidData,
                format!("claimed number is unreadable from {}", claim.path.display()),
            ))
        })?;

        // Assign the globally unique identity before anything is serialised. The
        // `id:` frontmatter line and the filename prefix both come from it, so it
        // must be fixed before `to_file_contents` and before `layout::render`. A
        // caller that already set one (an import, or a test) keeps it; this is the
        // single place every create path — CLI, MCP, TUI, sync — flows through.
        if issue.id.is_none() {
            issue.id = Some(crate::id::generate_issue_id());
        }

        // WP02 layout, now configurable ([layout] in tix.toml): the directory is
        // rendered from the configured template and may be nested; `filename_stem`
        // still overrides the filename for callers that pin a stem.
        let rel = crate::layout::render(&self.config.layout, issue);
        let (dir, file) = rel.rsplit_once('/').unwrap_or(("", rel.as_str()));
        std::fs::create_dir_all(self.issues_dir.join(dir))?;

        let stem = match filename_stem {
            Some(s) => s.to_string(),
            None => file.strip_suffix(".md").unwrap_or(file).to_string(),
        };
        // Serialised **after** the number is fixed, so the `number:` in the file is
        // the claimed one.
        let contents = issue.to_file_contents();

        let written = self.write_new_issue_file(dir, &stem, contents.as_bytes());
        // The claim is now permanent: the issue file exists, so that file — not the
        // marker — is the authority for the number, and dropping the marker would
        // reopen the window this exists to close. A create that *failed* releases
        // its claim instead, so a failure does not leak a number for nothing.
        match written {
            Ok((filename, path)) => {
                claim.commit();
                issue.filename = filename;
                self.reconcile_mentions(issue, &issue.filename);
                Ok(path)
            }
            Err(e) => {
                claim.release();
                Err(e)
            }
        }
    }

    /// Write **new** issue file, never overwriting an existing one.
    ///
    /// The stem was `{created}-{slugified title}` at the time of this bug (a
    /// new-schema name now also carries the issue id:
    /// `{created}-{id}-{slugified title}`), so it was a function of the issue's
    /// creation date, its title, and its assignee segment — three things routinely
    /// identical across two issues. Two `tix create --title "Same title"` runs on
    /// the same day therefore resolved to the **same path**, and `atomic_write`
    /// renames over the target, so the second create silently destroyed the first.
    /// No concurrency was required, and both commands reported success:
    ///
    /// ```text
    /// $ tix create --title "Same title" --priority high
    /// Created herbert-maschke/2026-09-28-same-title.md
    /// $ tix create --title "Same title" --priority low
    /// Created herbert-maschke/2026-09-28-same-title.md
    /// $ ls docs/issues/*/
    /// 2026-09-28-same-title.md            # one file
    /// $ tix list
    /// NUM  TITLE       STATUS  PRIORITY
    /// 2    Same title  todo    low       # issue #1 is gone
    /// ```
    ///
    /// Two layers, because the first alone is still a race:
    ///
    /// 1. **Probe** for a free name, appending `-2`, `-3`, … to the stem. This
    ///    handles the deterministic case, which is the common one.
    /// 2. **Create the file with `O_EXCL`** via [`write_file_new`]. Probing cannot
    ///    see a file another process creates between the probe and the write, and
    ///    `rename` overwrites unconditionally, so the final step is the one that
    ///    actually guarantees no clobber. Losing the race retries from step 1.
    ///
    /// Probing alone is the version that looks correct and is not: a second process
    /// that writes the same stem in the same millisecond would still be destroyed,
    /// and the retry-on-`AlreadyExists` below exists precisely because a reviewer
    /// should not have to take that on trust.
    pub(in crate::storage) fn write_new_issue_file(
        &self,
        segment: &str,
        stem: &str,
        contents: &[u8],
    ) -> Result<(String, PathBuf)> {
        const MAX_ATTEMPTS: usize = 1_000;
        let mut suffix = 1usize;
        for _ in 0..MAX_ATTEMPTS {
            let filename = if suffix == 1 {
                format!("{segment}/{stem}.md")
            } else {
                format!("{segment}/{stem}-{suffix}.md")
            };
            let path = self.issues_dir.join(&filename);
            match write_file_new(&self.issues_dir, &path, contents) {
                Ok(()) => {
                    journal_issue_change(Path::new(&filename), true);
                    return Ok((filename, path));
                }
                // Someone took this name between the probe and the write. The
                // collision is benign — it is only a *name* — so take the next one.
                Err(TixError::Io(e)) if e.kind() == std::io::ErrorKind::AlreadyExists => {
                    suffix += 1;
                }
                Err(e) => return Err(e),
            }
        }
        Err(TixError::Io(std::io::Error::new(
            std::io::ErrorKind::AlreadyExists,
            format!(
                "could not find a free filename for {segment}/{stem}.md in {MAX_ATTEMPTS} attempts"
            ),
        )))
    }

    /// The number for the next created issue: `max(number)` over the live
    /// issue set plus one, or `1` when no issues exist (issue #52 — no
    /// persisted counter to advance). Scanning the same list that every
    /// other command uses keeps number resolution conservative: reusing a
    /// number requires first deleting every higher-numbered issue.
    ///
    /// **The empty case is `1`, not `0`.** It used to be `0`, because `max()` over
    /// an empty set has no natural answer and `0` was the fallback — which made the
    /// first issue in every fresh repository `#0`, and that number is then
    /// indistinguishable from a sentinel, an uninitialised value, or a field that
    /// failed to read. Found by running the binary rather than reading the code
    /// (tix #1376); two places in the codebase had already written the opposite
    /// assumption into a comment, and a third had used `0` as a
    /// `HierarchyNode::NO_ISSUE_YET` marker.
    ///
    /// Only the empty case changes. With any issue present the answer is `max + 1`,
    /// which is unaffected — so no existing repository renumbers, and no migration
    /// is implied. (One real issue in this repository is numbered `0`, written
    /// before this fix; it keeps its number, because renumbering is a migration and
    /// the mission's doctrine makes those an escalation trigger.)
    pub(in crate::storage) fn resolve_next_number(&self) -> Result<u32> {
        // `list_all`, not `list`: an archived issue keeps its number forever.
        // Reading only the active set would let a `create` reuse the number of
        // the highest-numbered archived issue (issue #1492).
        let issues = self.list_all()?;
        match issues.iter().map(|i| i.number).max() {
            None => Ok(1),
            Some(max) => max
                .checked_add(1)
                .ok_or_else(|| TixError::InvalidInput("issue-number overflow".to_string())),
        }
    }

    /// Write `issue` over the file at `filename`, then reconcile the file's
    /// **location** with the configured `[layout]` (`move_on_change`).
    ///
    /// Returns the store-relative path the issue lives at afterwards — the same
    /// one in the common case, a new one when a templated field (status, type,
    /// assignee, cycle, …) now renders a different directory. **Every write path
    /// goes through here**, so no surface (CLI, MCP, TUI, triage, sync) can
    /// leave an issue at a path that disagrees with the layout.
    pub fn update(&self, filename: &str, issue: &Issue) -> Result<String> {
        validate_filename(filename)?;
        let path = self.issues_dir.join(filename);
        if !path.is_file() {
            return Err(TixError::NotFound(format!("file {filename}")));
        }
        // The retired `links:` key is not in the model, so re-serializing drops
        // it — and with it the `retired_links_key` finding, silently. The
        // consequence is that `tix lint` reports a problem, the user runs an
        // unrelated `tix edit`, and both the finding and the data vanish with no
        // notice. That is the defect; C-001's no-migration intent is not.
        //
        // The write still proceeds, because refusing would make tix unusable
        // across the repository: 1216 of 1290 issue files here carry `links:`.
        // What changes is that the removal is *disclosed*, naming the field and
        // the file, so nothing is lost quietly. Removing the key by hand first
        // silences this.
        if issue.has_retired_links_key {
            // Recorded on the store, not printed here. `eprintln!` inside a
            // library function is invisible to the MCP server and the TUI, so
            // the same operation produced different observable output per
            // surface, which `contracts/surface-parity.md` forbids.
            //
            // Drained at the three surface boundaries, not at each write path:
            // `main` for every CLI command, the MCP `serve` loop per request,
            // and the TUI event loop. Draining per command was tried and reached
            // only `link` and `edit`, so every other write path — `mv`,
            // `rollover`, planning, sync, the TUI, MCP — warned about nothing.
            // That was worse than the `eprintln!` it replaced, which fired from
            // inside `update` and so covered all of them. A count of write
            // paths is deliberately not stated here: it drifts, and a figure a
            // later reader trusts is worse than no figure. `tests/mcp.rs` pins
            // the behaviour instead, for `main` and the MCP server.
            retired_key_disclosure(filename);
        }
        let contents = issue.to_file_contents();
        atomic_write(&self.issues_dir, &path, contents.as_bytes())?;
        journal_issue_change(Path::new(filename), true);
        // Unconditional auto-migration: after any write, the file is moved to the
        // directory `[layout]` renders (subject only to `move_on_change`). A
        // legacy or mismatched path is migrated, not left behind.
        let relocated = self.reconcile_location(filename, issue)?;
        // The mention records name the issue by id and record the path they saw it at, so a
        // reconciliation after the move stores the path the issue actually lives at.
        self.reconcile_mentions(issue, &relocated);
        Ok(relocated)
    }

    /// Move the file at `filename` so its directory matches what `[layout]`
    /// renders for `issue`, when `move_on_change` is set and the directory
    /// differs. The basename (including the archived-marker dot) is preserved.
    /// Returns the relative path afterwards (unchanged when no move happens).
    pub(in crate::storage) fn reconcile_location(
        &self,
        filename: &str,
        issue: &Issue,
    ) -> Result<String> {
        if !self.config.layout.move_on_change {
            return Ok(filename.to_string());
        }
        let target_dir = crate::layout::render_directory(&self.config.layout, issue);
        let Some((old_dir, base)) = split_relative(filename) else {
            return Ok(filename.to_string());
        };
        if old_dir == target_dir {
            return Ok(filename.to_string());
        }
        let stem = base.strip_suffix(".md").unwrap_or(&base);
        let moved = self.move_issue_file(filename, &target_dir, stem)?;
        Ok(moved.to_string_lossy().to_string())
    }

    pub fn delete(&self, filename: &str) -> Result<()> {
        validate_filename(filename)?;
        let path = self.issues_dir.join(filename);
        if !path.is_file() {
            return Err(TixError::NotFound(format!("file {filename}")));
        }
        // Read the number **before** the file goes, so the claim ledger can be told
        // the number is free again (#1352).
        //
        // Releasing the claim is what preserves issue #52's documented behaviour:
        // the next number is re-derived from the live set, so deleting the
        // highest-numbered issue lets its number be reused. Without this the ledger
        // holds that number forever, the next create climbs past it, and the feature
        // stops working — which is a regression the existing test caught.
        //
        // The residual window, stated rather than hidden: if a `create` is in flight
        // holding this claim while the `delete` runs, the claim is released and a
        // later create could take the number too. That needs a delete and a create to
        // interleave, and it was *unconditionally* broken before this ledger existed;
        // the ledger removes the plain concurrent-create case, which is the one that
        // actually happens. Repairing the delete/create interleave would need a lock,
        // and this is the reason the ledger was chosen over one.
        let freed = std::fs::read_to_string(&path)
            .ok()
            .and_then(|text| frontmatter_number(&text));
        // The issue's canonical id, best-effort, for clearing its mention records. Read before
        // the file goes, and read through the same parse the rest of the store uses rather than
        // a second frontmatter scraper.
        let identity = self
            .get(IssueSelector::Filename(filename.to_string()))
            .ok()
            .and_then(|issue| issue.id);
        journal_record_write(&path);
        std::fs::remove_file(&path)?;
        journal_issue_change(Path::new(filename), false);
        if let Some(number) = freed {
            NumberClaim::release_number(&self.issues_dir, number);
        }
        if let Some(id) = identity {
            self.clear_mentions(&id);
        }
        // Best-effort cleanup of the `<slug>-assets/` dir (FR-008): the `.md`
        // removal is the contract, so an asset-dir removal failure is only
        // reported as a warning, never propagated.
        if let Some((segment, basename)) = split_relative(filename) {
            let stem = basename.strip_suffix(".md").unwrap_or(&basename);
            let slug = slug_from_stem(stem);
            let asset_dir = self
                .issues_dir
                .join(&segment)
                .join(format!("{slug}-assets"));
            if asset_dir.exists()
                && let Err(e) = std::fs::remove_dir_all(&asset_dir)
            {
                eprintln!(
                    "warning: failed to remove asset dir {}: {e}",
                    asset_dir.display()
                );
            }
        }
        Ok(())
    }

    /// Archive an issue: rename its file to a dot-prefixed name **in place**.
    ///
    /// The marker is the filename (issue #1492), so this is a rename within the
    /// same assignee segment (`x.md` ↔ `.x.md`) plus exactly one `## History`
    /// event. `number`, `status`, `created` and every other frontmatter field
    /// are left untouched, no data is dropped, and the file is never deleted or
    /// moved between directories.
    ///
    /// An already-archived issue is refused with the `already_archived`
    /// diagnostic rather than re-archived: the operation is not idempotent by
    /// design, because a second call would append a second audit entry for a
    /// mutation that did not happen.
    pub fn archive(&self, sel: &str) -> Result<Issue> {
        self.set_archived(sel, true)
    }

    /// Restore an archived issue: the inverse of [`Store::archive`].
    ///
    /// An active issue is refused with the `not_archived` diagnostic.
    pub fn restore(&self, sel: &str) -> Result<Issue> {
        self.set_archived(sel, false)
    }

    pub(in crate::storage) fn set_archived(&self, sel: &str, archive: bool) -> Result<Issue> {
        // `resolve_issue` → `parse_selector` → `list_all`, so an archived issue
        // resolves here even though the default view hides it.
        let mut issue = self.resolve_issue(sel)?;
        if issue.archived == archive {
            return Err(TixError::InvalidInput(format!(
                "{}: issue #{} ({}) is already {}",
                if archive {
                    "already_archived"
                } else {
                    "not_archived"
                },
                issue.number,
                issue.filename,
                if archive { "archived" } else { "active" },
            )));
        }
        let old_rel = issue.filename.clone();
        let new_rel = flip_archived(&old_rel, archive).ok_or_else(|| {
            TixError::InvalidInput(format!(
                "cannot {} {old_rel}: its filename does not carry the archived marker in the \
                 expected position",
                if archive { "archive" } else { "restore" }
            ))
        })?;
        let old_path = self.issues_dir.join(&old_rel);
        let new_path = self.issues_dir.join(&new_rel);
        if !old_path.is_file() {
            return Err(TixError::NotFound(format!("file {old_rel}")));
        }
        if new_path.exists() {
            return Err(TixError::InvalidInput(format!(
                "cannot {} {old_rel}: {new_rel} already exists",
                if archive { "archive" } else { "restore" }
            )));
        }
        // Rename first: it is atomic, stays in the same directory, and cannot
        // lose content. Only then is the audit event written, at the new name.
        // A failure between the two leaves the file renamed but without the
        // event — never a duplicate, never lost data.
        //
        // The rename is recorded in the write journal (#1580), so a command-level
        // `Store::transaction` around `tix archive`/`tix restore` can undo it: the
        // event write below is a *second* mutation, and a failure there must put
        // the file back at its active name rather than leave it archived without
        // its audit entry.
        journal_record_move(&old_path, &new_path);
        std::fs::rename(&old_path, &new_path)?;
        issue.filename = new_rel.clone();
        issue.archived = archive;
        issue.history.append_now(
            &actor_identity(),
            if archive {
                HistoryEventKind::Archived
            } else {
                HistoryEventKind::Restored
            },
            &format!("{old_rel} -> {new_rel}"),
        );
        // No `bump_updated`: `updated` is a frontmatter field and archiving must
        // leave every frontmatter field byte-identical.
        issue.filename = self.update(&new_rel, &issue)?;
        Ok(issue)
    }

    /// Physically move an issue file into the assignee segment of a new
    /// assignee (FR-031, `contracts/file-format.md` rule 9).
    ///
    /// `filename` is a path relative to the issues dir: either a legacy flat
    /// basename (`2026-05-10-fix-login.md`, C-010) or a grouped path
    /// (`alice/2026-05-10-fix-login.md`). It is validated via the relaxed
    /// [`validate_filename`] before anything touches the filesystem, so
    /// traversal attempts are refused here as everywhere else.
    ///
    /// The old assignee segment is read from the current relative path, the
    /// new one derived with [`derive_segment`]; equal segments are a no-op.
    /// The target filename keeps the original `created-slug` stem; when the
    /// target already holds `<stem>.md`, a deterministic `-1`, `-2`, …
    /// suffix is appended by testing existence — an existing file is never
    /// overwritten or deleted. `number`/`created` live in the frontmatter and
    /// are untouched, so issue-number stability is guaranteed by construction
    /// (C-007).
    ///
    /// The move is a single `std::fs::rename` (atomic-ish, same filesystem).
    /// Returns the **new relative path** (matching how `issue.filename` is
    /// stored) on success, including the unchanged relative path for the
    /// equal-segment no-op.
    pub fn reassign(&self, filename: &str, new_assignee: Option<&str>) -> Result<PathBuf> {
        // `get` validates `filename` and errors NotFound when it is missing.
        let issue = self.get(IssueSelector::Filename(filename.to_string()))?;
        let mut updated = issue.clone();
        updated.assignee = new_assignee.map(str::to_string);
        let target_dir = crate::layout::render_directory(&self.config.layout, &updated);
        let (old_dir, base) = split_relative(filename).ok_or_else(|| {
            TixError::InvalidInput(format!("invalid relative issue filename: {filename}"))
        })?;
        if old_dir == target_dir {
            return Ok(PathBuf::from(filename));
        }
        let stem = base.strip_suffix(".md").unwrap_or(&base);
        self.move_issue_file(filename, &target_dir, stem)
    }

    /// Relocate an issue file to an exact store-relative `target` (used by
    /// `tix layout migrate`). Frontmatter and number are preserved because
    /// nothing is rewritten — it is a rename; an occupied target is refused; the
    /// `<slug>-assets/` dir moves alongside.
    pub fn migrate_issue(&self, filename: &str, target: &str) -> Result<()> {
        if target == filename {
            return Ok(());
        }
        validate_filename(target)?;
        let from = self.issues_dir.join(filename);
        if !from.is_file() {
            return Err(TixError::NotFound(format!("file {filename}")));
        }
        let to = self.issues_dir.join(target);
        if to.exists() {
            return Err(TixError::InvalidInput(format!(
                "cannot migrate {filename}: {target} already exists"
            )));
        }
        if let Some(parent) = to.parent() {
            std::fs::create_dir_all(parent)?;
        }
        std::fs::rename(&from, &to)?;
        let (old_dir, base) = split_relative(filename).unwrap_or_default();
        let stem = base.strip_suffix(".md").unwrap_or(&base);
        let asset_name = format!("{}-assets", slug_from_stem(stem));
        let old_asset_dir = self.issues_dir.join(&old_dir).join(&asset_name);
        if old_asset_dir.exists()
            && let Some(new_dir) = to.parent()
        {
            let moved = resolve_asset_dir_name(new_dir, &asset_name);
            std::fs::rename(&old_asset_dir, new_dir.join(&moved))?;
        }
        Ok(())
    }

    /// Move an issue file (and its `<slug>-assets/` dir) from `filename` to
    /// `<target_dir>/<stem>[-N].md`, creating the directory as needed. A target
    /// collision takes the first free `-N` suffix; nothing is overwritten.
    pub(in crate::storage) fn move_issue_file(
        &self,
        filename: &str,
        target_dir: &str,
        stem: &str,
    ) -> Result<PathBuf> {
        let target_dir_path = self.issues_dir.join(target_dir);
        std::fs::create_dir_all(&target_dir_path)?;
        let new_name = resolve_target_name(&target_dir_path, stem);
        let old_dir = split_relative(filename).map_or_else(String::new, |(d, _)| d);
        let from = self.issues_dir.join(filename);
        let to = target_dir_path.join(&new_name);
        journal_record_move(&from, &to);
        std::fs::rename(from, to)?;
        journal_issue_change(Path::new(filename), false);
        journal_issue_change(Path::new(&format!("{target_dir}/{new_name}")), true);
        // Move the `<slug>-assets/` dir alongside the file (FR-007). On a
        // same-named dir in the target, disambiguate rather than overwrite.
        let slug = slug_from_stem(stem);
        let asset_name = format!("{slug}-assets");
        let old_asset_dir = self.issues_dir.join(&old_dir).join(&asset_name);
        if old_asset_dir.exists() {
            let moved = resolve_asset_dir_name(&target_dir_path, &asset_name);
            let asset_target = target_dir_path.join(&moved);
            journal_record_move(&old_asset_dir, &asset_target);
            std::fs::rename(&old_asset_dir, &asset_target)?;
        }
        Ok(PathBuf::from(format!("{target_dir}/{new_name}")))
    }

    /// Move an issue to the directory its templated fields now render to, when
    /// `move_on_change` is set. The basename is preserved. Returns whether it
    /// moved; a no-op when already in place or when `move_on_change` is off.
    pub fn move_to_layout(&self, issue: &mut Issue) -> Result<bool> {
        let before = issue.filename.clone();
        let after = self.reconcile_location(&before, issue)?;
        issue.filename = after.clone();
        Ok(after != before)
    }

    /// Copy an asset into the issue's `<slug>-assets/` directory (FR-006) and
    /// insert a relative markdown link at the end of the body, persisted via
    /// [`Store::update`] (NFR-004).
    ///
    /// The asset dir is derived from the issue filename per
    /// `contracts/comments-format.md`: `<slug>-assets/` where `<slug>` is the
    /// basename stem minus the leading `YYYY-MM-DD-` date prefix. The copy is
    /// atomic (temp + rename, NFR-004); on a name collision the file is stored
    /// as `<stem>-<n>.<ext>` (first free `n`) and the inserted link points at
    /// the actual written name. Image extensions (`.png` `.jpg` `.jpeg`
    /// `.gif` `.svg` `.webp` `.bmp`) get the `![…](…)` form, everything else
    /// the `[…](…)` form. The link path is relative to the issue file, so the
    /// segment prefix is never part of it.
    pub fn add_asset(&self, filename: &str, source_path: &Path) -> Result<AssetAdded> {
        validate_filename(filename)?;
        let mut issue = self.get(IssueSelector::Filename(filename.to_string()))?;

        let (segment, basename) = split_relative(filename).ok_or_else(|| {
            TixError::InvalidInput(format!("invalid relative issue filename: {filename}"))
        })?;
        let stem = basename
            .strip_suffix(".md")
            .ok_or_else(|| {
                TixError::InvalidInput(format!(
                    "asset target must be a `.md` issue file: {filename}"
                ))
            })?
            .to_string();
        let slug = slug_from_stem(&stem);
        let dir_name = format!("{slug}-assets");
        let asset_dir = self.issues_dir.join(&segment).join(&dir_name);
        std::fs::create_dir_all(&asset_dir)?;

        let source_name = source_path
            .file_name()
            .and_then(|n| n.to_str())
            .ok_or_else(|| {
                TixError::InvalidInput("asset source must have a file name".to_string())
            })?
            .to_string();
        let written_name = resolve_asset_name(&asset_dir, &source_name);
        atomic_copy(&asset_dir, &asset_dir.join(&written_name), source_path)?;

        let label = written_name
            .rsplit_once('.')
            .map(|(stem, _)| stem)
            .unwrap_or(&written_name);
        let link = if is_image_name(&written_name) {
            format!("![{label}]({dir_name}/{written_name})")
        } else {
            format!("[{label}]({dir_name}/{written_name})")
        };

        // Append the link as a new line at the end of the body, reusing the
        // comment-appender newline discipline so the description is never
        // rewritten (FR-007).
        if !issue.body.is_empty() {
            if !issue.body.ends_with('\n') {
                issue.body.push('\n');
            }
            if !issue.body.ends_with("\n\n") {
                issue.body.push('\n');
            }
        }
        issue.body.push_str(&link);
        issue.body.push('\n');
        issue.bump_updated();
        self.update(filename, &issue)?;

        Ok(AssetAdded { link, written_name })
    }
}