chore(workflow): plan stacked migration PRs

docs/plans/2026-06-09-004-chore-workflow-owned-merge-stacked-prs-plan.md

@@ -0,0 +1,65 @@
+---
+title: "chore: Workflow-owned merge stacked PR creation"
+type: chore
+status: active
+date: 2026-06-09
+depth: shallow
+origin: docs/plans/2026-06-09-003-refactor-workflow-owned-merge-full-migration-slices-plan.md
+---
+
+# chore: Workflow-owned merge stacked PR creation
+
+## Summary
+
+Create a linear GitHub PR stack for the remaining workflow-owned merge,
+retry, scheduling, recovery, projection, deletion, and release slices. The stack
+does not claim future implementation is complete. Each PR carries a durable
+slice handoff document and is opened as a draft against the previous slice
+branch so reviewers can see ordering, dependency, and milestone intent.
+
+## Requirements Trace
+
+- R1. Every migration slice S0-S18 from the origin plan is represented in the
+  PR stack.
+- R2. Existing PR #1571 remains the stack base for S0/S1.
+- R3. Remaining slices S2-S18 each receive a dedicated branch and draft PR.
+- R4. Each branch has a non-empty, reviewable diff that records the slice goal,
+  milestone, dependencies, file scope, tests, and exit gate.
+- R5. PR bodies link back to the full migration plan and identify their base
+  branch so the stack is reconstructible.
+
+## Scope
+
+In scope:
+
+- Add `docs/plans/workflow-owned-merge-stack/sXX-*.md` handoff files.
+- Create and push one branch per remaining slice.
+- Open draft PRs stacked linearly from S2 through S18.
+- Update PR #1571 with the complete slice/milestone list when needed.
+
+Out of scope:
+
+- Implementing S2-S18 code changes in this turn.
+- Merging the stack.
+- Rewriting existing PR #1571 commits.
+
+## Stack Shape
+
+- S0/S1: existing PR #1571, branch
+  `feature/workflow-owned-merge-retry-scheduling-plan`, base `main`.
+- S2: base S0/S1 branch.
+- S3-S18: each branch is based on the immediately preceding slice branch.
+
+This is intentionally linear even though the origin dependency graph has some
+parallelizable edges. A linear stack gives GitHub a straightforward review and
+landing path; implementation branches can still be split or rebased later if a
+slice needs to move independently.
+
+## Verification
+
+- `git status --short --branch` is clean after all branches are pushed.
+- `gh pr view` succeeds for each created PR.
+- Every created PR body includes the slice number, milestone, dependency, full
+  plan link, and base branch.
+- `gh pr checks` is inspected for the current stack base and any newly opened
+  PR checks that are immediately available.