The Changes / Files-changed tab showed nothing for multi-repo workspace tasks:
the task-diff backend is single-repo throughout, and a workspace task has null
task.worktree/task.branch (its per-repo state lives in workspaceWorktrees), so
every path fell back to git-diff against the non-git workspace root → empty.
Backend (register-session-diff-routes): extract the single-repo per-worktree
detailed-diff into one shared helper (computeWorktreeDetailedFiles) and add a
workspace branch to BOTH /tasks/:id/diff and /tasks/:id/file-diffs that runs
before the single-repo logic: iterate sorted workspaceWorktrees, compute each
sub-repo's diff in its own live worktree against that repo's baseCommitSha (done
tasks fall back to the per-repo landed range in the sub-repo root), and aggregate
with `${repoRel}/`-prefixed paths. Single-repo behavior is byte-for-byte
preserved (renamed→modified fold retained; 58 existing diff-route tests pass).
Frontend: TaskChangesTab takes an isWorkspace prop and no longer shows the
single-repo "No worktree available" empty state for workspace tasks;
TaskDetailModal passes isWorkspace={isWorkspaceTask(workingTask)}.
Tests: backend aggregation (repo-prefixed paths + stats) and frontend rendering
of workspace changes instead of the empty state.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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