Stack view shows "not ready" / "unable to merge as a stack" on approved mergeable PRs (stale stack UI cache)

No repository files or tests are named. Start by reproducing the 13-level stack in GitHub's native stack view and compare its displayed readiness with the REST and GraphQL fields listed in the report; done means the UI reflects the approved, mergeable PRs and enables "Merge stack (13)".

Summary

The GitHub stack view (native stack feature, not CLI) shows "not ready" on some PRs in a 13-level stack, and displays "unable to merge as a stack" globally, even though every PR in the stack reports mergeable=MERGEABLE, mergeStateStatus=CLEAN (or UNSTABLE), reviewDecision=APPROVED, and all status checks passing via both REST and GraphQL APIs.

Stack structure (anonymized)

base-branch
 └── feat/base            → PR #1 (base: base-branch)           ← trunk base
  └── feat/layer-2        → PR #2 (base: feat/base)
   └── feat/layer-3       → PR #3 (base: feat/layer-2)
    └── feat/layer-4      → PR #4 (base: feat/layer-3)
     └── feat/layer-5     → PR #5 (base: feat/layer-4)
      └── feat/layer-6    → PR #6 (base: feat/layer-5)
       └── feat/layer-7   → PR #7 (base: feat/layer-6)
        └── feat/layer-8  → PR #8 (base: feat/layer-7)
         └── feat/layer-9 → PR #9 (base: feat/layer-8)
          └── feat/layer-A → PR #10 (base: feat/layer-9)
           └── feat/layer-B → PR #11 (base: feat/layer-A)
            └── feat/layer-C → PR #12 (base: feat/layer-B)
             └── feat/layer-D → PR #13 (base: feat/layer-C)

13 PRs in total. The bottom PR targets base-branch; each subsequent PR targets its predecessor's branch. All PRs are open, non-draft, created via gh stack submit.

Environment

• gh 2.97.0
• gh-stack v0.1.0
• Repository: private, no branch protection, no repository rulesets, no merge queue, no CODEOWNERS.
• "Dismiss stale pull request approvals when new commits are pushed": disabled.

Observed behavior

In the GitHub stack UI (native stack view)

• Bottom 7 PRs (#1–#7): show "Ready"
• PR #8: shows "Not ready" (no tooltip / reason shown)
• PR #9: shows "Blocked downstack"
• PR #10: shows "Not ready" (no tooltip / reason shown)
• PRs #11–#13: show "Blocked downstack"
• At the top: global message "Unable to merge as a stack"

Via the API (both REST and GraphQL, confirmed multiple times over several minutes)

Every PR in the stack (including #8 and #10) consistently reports:

Field	Value
mergeable	MERGEABLE
mergeStateStatus	CLEAN (or UNSTABLE — only non-required checks pending like CodeRabbit)
reviewDecision	APPROVED (multiple approvals from different reviewers)
statusCheckRollup.state	SUCCESS
isDraft	false
requested_reviewers	[] (no pending reviewer requests)
No branch protection	(none exists on any branch in the stack)
No repository rulesets	(none exist)

GraphQL query used:

{
  repository(owner: "O", name: "R") {
    pullRequest(number: N) {
      mergeable
      mergeStateStatus
      reviewDecision
      isDraft
      statusCheckRollup { state }
    }
  }
}

Context about the "not ready" PRs (#8 and #10)

• Both are history-import PRs — they contain 500+ commits each (preserved full history of the imported repositories), adding ~48k lines across 180+ files.
• The remaining PRs are smaller (single-digit to low-double-digit commits).
• All PRs (including #8 and #10) were created via the same gh stack submit flow, all with the same review/check configuration.
• The status checks on #8 and #10 all show green/success. Only CodeRabbit (not required) shows as not completed.

Attempted workaround: close + reopen the "not ready" PRs

We closed and reopened PR #8 (the first "not ready" PR in the stack) to force a full server-side recompute:

gh pr close 8 && gh pr reopen 8

Result:

• The individual PR returned to mergeable=MERGEABLE, reviewDecision=APPROVED correctly.
• The stack view took ~30 seconds to reload, but the state did not change: PR #8 remained "not ready", PR #9 remained "blocked downstack", and the global message stayed "unable to merge as a stack".

Close+reopen did not invalidate the stack view's cached state. The stack view appears to maintain its own independent cache that is not invalidated by PR state changes.

Expected behavior

Given that:

1. All PRs are mergeable (no conflicts, MERGEABLE).
2. All PRs are approved (APPROVED).
3. All required status checks pass (SUCCESS).
4. No branch protection, rulesets, CODEOWNERS, or merge queue block merging.
5. Close+reopen did not help.

GitHub's native stack view should reflect the actual PR state and show all 13 PRs as "Ready", with the "Merge stack (13)" option enabled and functional. A stale cached state rendering the stack unmergeable is a blocking UX bug.

Related

• #323 — "Can't merge a stacked PR with no clear reason (all PRs show mergeable)". Same class of bug: stack UI state differs from API state. In our case the stack never shows as mergeable at all (no attempt to merge fails — the UI never allows the attempt). We confirm the MERGEABLE/CLEAN/APPROVED symptom. Our close+reopen attempt did not resolve it, suggesting a different cache invalidation path.