fix: require lossless backlog handoff support

[gizm0duck]

What Changed

• Require tasks-axi 0.2.2+ with full-detail reads, lossless body replacement and archival, and atomic multi-item moves before treating the backlog backend as compatible.
• Guard secondmate backlog handoffs against incompatible tooling and add round-trip coverage for preserving structured fields, bodies, links, dependencies, holds, and neighboring tasks.
• Centralize the compatibility contract in configuration docs and align bootstrap, session-start, teardown, and backend regression fixtures with it.

Risk Assessment

✅ Low: Captain, the change is well-bounded and consistently strengthens tasks-axi compatibility checks without introducing a substantiated functional risk.

Testing

Completed 1 recorded test check.

• Outcome: 🔧 1 issue found → auto-fixed ✅ across 2 runs (32m29s)

Pipeline

Updates from git push no-mistakes

⏭️ **intent** - skipped

✅ No issues found.

🔧 **Rebase** - 1 issue found → auto-fixed ✅

• ⚠️ tests/fm-backend.test.sh - merge conflict rebasing onto origin/main

🔧 Fix applied.
✅ Re-checked - no issues remain.

✅ **Review** - passed

✅ No issues found.

🔧 **Test** - 1 issue found → auto-fixed ✅

• 🚨 tests failed with exit code 1
• command -v tmux >/dev/null || { echo "tmux is required for e2e tests" >&2; exit 1; }; tmux -V; rc=0; for t in tests/*.test.sh; do echo "== $t =="; bash "$t" || rc=1; done; exit "$rc"

🔧 Fix: Update compact tasks-axi compatibility fixture
✅ Re-checked - no issues remain.

• command -v tmux >/dev/null || { echo "tmux is required for e2e tests" >&2; exit 1; }; tmux -V; rc=0; for t in tests/*.test.sh; do echo "== $t =="; bash "$t" || rc=1; done; exit "$rc"

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.

[kunchenguid]

Automated reminder: thanks for the PR! This branch currently has a merge conflict with the base branch.

When you get a chance, please rebase onto (or merge) the latest base branch, resolve the conflict, and push. After that, checks will re-run and the PR will get looked at again.

_{Noted for firstmate#632 at 4c781eaf.}

[gizm0duck]

I was struggling to get firstmate working properly after switching the harness from Claude to Codex and subsequently updating firstmate. These changes came as a result of that switch and the resulting conversation with firstmate.

[gizm0duck]

Rebased onto current upstream main at head af947f12120dc543bfe3f5f38dff93481fb4f1f3. The no-mistakes rerun passed automated review, the full repository test suite, documentation review, and pinned ShellCheck lint. GitHub created the updated fork workflows but left the CI and Require no-mistakes runs in action_required; an upstream maintainer needs to approve those hosted runs for this head.

[kunchenguid]

Automated reminder: thanks for the PR! This branch currently has a merge conflict with the base branch.

When you get a chance, please rebase onto (or merge) the latest base branch, resolve the conflict, and push. After that, checks will re-run and the PR will get looked at again.

_{Noted for firstmate#632 at af947f12.}