[danbarua]

Problem

#673 made File Explorer open the folders above the open file, but only when the open file's address is in the tree at HEAD (/workspace/{slug}/file/{path}). A commit's changed files and the graph's file nodes open a file as it was at that commit (/workspace/{slug}/commit/{id}/file/{path}). File Explorer had no row for that address, so its folders stayed closed. #673's test opened the HEAD address directly, so it did not catch this.

Change

• API. A file read at a commit links the same path at HEAD as head, when the tree at HEAD holds a file there. A file read at HEAD has no head link.
• File Explorer. It follows the open file's head link: it opens that path's folders and marks its row with the box. A file open at HEAD is followed as before.

Controls

• A file HEAD no longer holds, such as one deleted later, has no head link, so File Explorer opens no folders and marks no row.
• The marked row is the HEAD file. File Explorer marks the file at HEAD, while the centre shows the file as it was at the commit.

Verification

• bun run check: exit 0, 1105 pass, 0 fail.
• bun run e2e with E2E_PORT_API=9019 E2E_PORT_DEV=8970 E2E_PORT_BUILT=8971: 175 passed, 11 skipped (the dev-only tests, in the built bundle).
• Unit test (tests/git-api.test.ts): src/a.ts at the first commit links head to /workspace/alpha/file/src/a.ts. data/blob.bin at the first commit, dropped later, has no head link. src/a.ts read at HEAD has no head link.
• e2e (dev server and built bundle): with File Explorer and Source Explorer open, opening the commit "Change a, plan the work" and clicking its changed file notes/plan.md opens the commit's version (/commit/{id}/file/notes/plan.md). It also opens notes in File Explorer, and marks plan.md.

Linked issues

None. Follows #673.

🤖 Generated with Claude Code