feat(plan): rewrite plan-level.yaml for platform-native PR review (P7b-i-d)

[PolyphonyRequiem]

Summary

Phase 3 P7b-i-d. Rewrites plan-level.yaml from v1.0.1 to v2.0.0, replacing in-workflow LLM-verdict planning loop (technical_reviewer / readability_reviewer / review_router / plan_approval) with the platform-native PR-review flow built on the substrate verbs from P7b-i-a / b / c plus the four prior plan/branch/pr verbs.

This is the consumer flip for everything Phase 3 has been building toward.

Lifecycle

depth_guard -> guidance_loader -> root_resolver -> type_loader
            -> ancestor_chain -> state_detector
              |
              +-- not_started      -> architect -> write_plan -> ensure_plan_branch
              |                     -> commit_and_push -> open_plan_pr
              |                     -> plan_reviewer (advisory)
              |                     -> poll_status (single-shot)
              +-- awaiting_review  -> poll_status
              +-- stale_generation -> architect (re-author)
              +-- merged_unseeded  -> seeder -> child_router (recurse)
              +-- complete         -> child_router (recurse only)
              +-- closed_unmerged  -> blocked exit

poll_status:
  approved + no parent change -> merge_plan_pr -> seeder
  approved + parent change    -> parent_change_blocked_exit (P8 stub)
  changes_requested           -> revise_counter -> architect (cap 5)
  pending                     -> pending_review_gate
  merged                      -> seeder
  closed                      -> closed_unmerged_gate

Design decisions

Tracks files/p7-design-doc.md:

ID	Decision
Q1	plan path = plans/plan-{item_id}.md (handled by write-plan verb)
Q2	single advisory plan_reviewer + human approval (option 2)
Q3	DEVIATION -- in-workflow human_gate for pending (option a) instead of exit-with-pending (option b). polyphony-full's outer state_detector still uses the OLD single-string phase model and would infinite-loop on awaiting_review. Switch to (b) lands with Phase 2c YAML migration.
Q4	root_resolver derives root_id once via polyphony root resolve; all downstream verbs read root_resolver.output.resolved_root_id
Q5	plan_reviewer is a script agent calling gh pr review --comment once and returning
Q6	revise loop capped at 5 with revise_cap_gate escalation
Q7	blocked exits via human_gate Markdown (no per-workflow output schema yet)
Q8	requests_parent_change: true rejected with honest "P8 not implemented" gate

Preserved from v1

• Architect output schema ({plan, children, open_questions, summary}) -- existing architect-plan-level.md prompt unchanged
• open_questions policy machinery (open_questions_policy / _counter / _answer_counter / _gate)
• Recursive child planning via plan_children_group for_each
• depth_guard with cap 6
• All gates: depth_exceeded_gate, open_questions_gate, plan_children_summary_gate

Substrate verbs consumed

All shipped in prior PRs (#83, #85, #86, #88 + earlier P7b-i-a/b/c):

• polyphony root resolve
• polyphony plan derive-ancestor-chain
• polyphony plan detect-state
• polyphony plan write-plan
• polyphony plan commit-and-push
• polyphony plan seed-children
• polyphony plan next-child
• polyphony branch ensure-plan
• polyphony pr open-plan-pr
• polyphony pr poll-status
• polyphony pr merge-plan-pr
• polyphony policy resolve --domain open_questions

Drive-by build fix

PR #88 (P7b-i-c detect-state) added IGitClient and IGhClient to the PlanCommands constructor but didn't update PlanCommandsWritePlanTests.CreateCommand(). Main has been red since that merge. This PR brings the suite back to 1809/1809 green.

Validation

Check	Result
dotnet test	1809/1809 pass (was: build break on main)
lint-plan-level.ps1	10/10 checks pass
lint-plan-level.Tests.ps1	5/5 Pester tests pass
lint-strict-undefined.ps1	10 workflows scanned clean
lint-type-agnostic.ps1 -Surface all	42 files scanned clean
lint-root-routing.ps1	7 phases / 3 sub-workflows validated

Out of scope

• lint-implement-pg.ps1 expects claude-opus-4.7-1m-internal but YAML has claude-opus-4.6 / claude-opus-4.7. Same failure on main; tracked separately.
• P8 scope renegotiation (requests_parent_change) -- gates with honest error
• P9 ancestor cascade (stale_generation post-merge) -- gates with stub
• P10 audit/UX polish -- not started

Next steps after merge

1. Smoke-test on a real ADO work item (single-level plan first; then depth-2)
2. P8 -- requests_parent_change cascade
3. P9 -- ancestor cascade auto-rebase
4. Migrate polyphony-full's state_detector to requirement+disposition shape (Phase 2c) so we can flip Q3 to option b