Report a stopped rebase from Go #897

Problem

The report at packages/agents/source/skills/rebase/shared/scripts/rebase-status.sh:43 identifies the stopped patch, stage-based conflict kinds and paths staged without stopping. It shares marker rules with continuation. A separate port keeps state-changing behavior out of this report's review.

Part of #588 and #326.

Acceptance criteria

1. AC1: Given no active rebase, when status is requested, then the frozen no-rebase report and status are returned.
2. AC2: Given an apply-backend rebase, when status is requested, then it reports that this workflow does not drive that backend.
3. AC3: Given a merge-backend stop, when status is requested, then branch, target, progress and patch details match the frozen report.
4. AC4: Given content, add/add or delete/modify stages, when status is requested, then each path has the frozen kind and side description.
5. AC5: Given paths staged without a conflict, when status is requested, then they appear in the frozen staged-without-stopping report.
6. AC6: Given marker candidates, when status is requested, then its worktree-marker report preserves the scanner's exemptions and failure diagnostic.
7. AC7: Given remaining instructions or a stop with no unmerged paths, when status is requested, then its next-step report matches the frozen implementation.
8. AC8: Non-functional: status leaves contents, index, refs and recovery evidence unchanged.
9. AC9: Non-functional: native report cases execute without skips on macOS, Linux and Windows.

Scope and non-goals

Scope: the stopped-rebase report under agentrepo rebase.

Non-goal: resolving, continuing, implementing a scanner, or porting guards. Keep shell and coupled Python frozen through N-2, with no new shell logic. Do not switch callers or retire tests in this child.

Approach

Reuse child 01's context and internal/agentrepo/markers.go:88. Preserve stage interpretation at packages/agents/source/skills/rebase/shared/scripts/rebase-status.sh:93 and candidate selection at packages/agents/source/skills/rebase/shared/scripts/rebase-status.sh:131. Pin actual exit behavior: a merge-backend report with all paths resolved reaches normal success, despite the broader header description.

Dependencies

Blocked by: #895, #753.

Size

S. Forecast 470 code lines: 200 implementation, 240 tests and fixtures, 30 registration. Measured source baseline: 109 code lines. Prose allowance: 180 lines.

scc could not run in the isolated checkout. Measured baselines count non-blank lines other than full-line # comments, including Python docstrings and embedded code conservatively. Forecasts include implementation, tests, fixtures and registration; they are estimates, not measured future Go. Generated output is excluded only under packages/agents/claude/.apm/skills/, packages/agents/codex/.apm/skills/, .claude/skills/, .agents/skills/ and tokens.json. The source under packages/agents/source/ and copies anywhere else count. The final diff must be at most 800 code lines and 2,000 prose lines, with no exception; split before implementation if either forecast grows beyond its limit.

Verify plan

• AC1, AC2, AC3, AC7: compare reports/statuses for no replay, apply backend, conflicts, edit/break stops, absent metadata and resolved stops.
• AC4, AC5: construct stage combinations and rerere-enabled/disabled staged-path sets and compare labels.
• AC6: reuse scanner fixtures and inject scanner failure as covered at tests/skills/rebase/scripts/marker-scan.bats:28.
• AC8: snapshot repository state around each report.
• AC9: inspect executing native cases on all three CI platforms.
• Definition of done: D1 each AC is verified at the merged head, with the commands and results cited in the pull request's Verification. D2 an independent review approves the exact merged head, and every finding has a recorded disposition. D3 required checks pass with no gate loosened. D4 the leak scans the repository specifies are clean, and every post made for this work passes the per-post leak review before it is posted. D5 every commit is signed. D6 the documentation matches the change or the Verification says why there is no impact. D7 every commit has an Assisted-by trailer and the pull request has the provenance:agent-assisted label. D8 the pull request stays within the size limits. D9 follow-ups are filed as issues and listed under Related. D10 the merge closes the issue through a closing reference, the board shows Done, and the final Status: comment names the merge commit.

Risks

Wrong side labels or hidden rerere results encourage incorrect resolutions. Undo: revert the new report; frozen callers remain available.

Operator authority

None.