fix: surface remote GitHub base conflicts

[dubscode]

Summary

• refresh tracked root branches from origin/<root> before post-merge restacks children
• surface remote-base-mismatch in dub doctor when the remote PR head is not descended from the GitHub base branch
• make dub merge-check fail when GitHub still reports the PR as conflicting
• document the safer recovery and verification flow

Fix Details

• post-merge now fetches and fast-forwards each tracked root before replaying descendants, and fails explicitly if the trunk cannot be fast-forwarded safely.
• doctor now checks the remote PR head against the GitHub base branch via baseRefName, so a stale remote base shows up before users trust a false-clean local state.
• merge-check now verifies GitHub mergeability in addition to stack order.

Verification

• pnpm checks
• pnpm typecheck
• env -u DUBSTACK_BEDROCK_AWS_PROFILE -u DUBSTACK_BEDROCK_AWS_REGION -u DUBSTACK_BEDROCK_MODEL -u DUBSTACK_GEMINI_API_KEY -u DUBSTACK_AI_GATEWAY_API_KEY -u GOOGLE_CLOUD_PROJECT pnpm test

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
dubstack	Skipped		Mar 10, 2026 4:24am

[Copilot]

Pull request overview

This PR improves DubStack’s ability to detect and prevent “false clean” stacks when local or remote bases drift from what GitHub is actually evaluating, and tightens merge gating based on GitHub’s conflict/mergeability signals.

Changes:

• Add GitHub PR mergeability query support and use it in dub merge-check.
• In post-merge, refresh/fast-forward tracked root branches from origin/<root> before restacking descendants.
• Extend dub doctor with a new remote-base-mismatch issue and document recovery/verification steps.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/cli/src/lib/github.ts	Adds getPrMergeStatusByNumber() to query mergeable + mergeStateStatus via gh.
packages/cli/src/lib/github.test.ts	Adds tests for getPrMergeStatusByNumber().
packages/cli/src/commands/post-merge.ts	Fetches and fast-forwards each stack root from origin/<root> before restack.
packages/cli/src/commands/post-merge.test.ts	Updates mocks/assertions and adds a fast-forward failure test.
packages/cli/src/commands/merge-check.ts	Fails merge-check when GitHub reports conflicting/dirty.
packages/cli/src/commands/merge-check.test.ts	Adds coverage for failing on conflicting/dirty mergeability.
packages/cli/src/commands/doctor.ts	Adds remote-base-mismatch detection using GitHub baseRefName vs remote ancestry.
packages/cli/src/commands/doctor.test.ts	Adds a repro-focused test for remote-base-mismatch.
apps/docs/content/docs/commands/doctor.mdx	Documents the new remote-base drift check and recommended recovery flow.
README.md	Updates doctor/merge-check docs and troubleshooting guidance.
QUICKSTART.md	Updates command descriptions to include GitHub mergeability verification.

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