feat(merge): _merge_no_ff_external for gh-pr-* branches (Phase 2)
External GitHub fork PRs need their contributor commit SHA in main's history
for GitHub's "merged" badge to fire. Cherry-pick rewrites the SHA, breaking
that detection. New _merge_no_ff_external function preserves the SHA via a
true merge commit.
Mechanics (mirrors _cherry_pick_onto_main shape):
1. Fetch origin/main + origin/{branch}
2. Detached worktree at origin/main, git merge --no-ff origin/{branch}
with verbose message: "Merge external GitHub PR #{N}: {branch_slug}"
3. Force-push merge commit M as origin/{branch}, replacing branch tip
4. Dispatch's existing ff-push origin/{branch} → main propagates M to main
M has parents [main_sha, contributor_sha]. M is a fast-forward descendant
of main_sha (first-parent chain), so the ff-push to main is valid without
--force. Contributor SHA reachable from main → GitHub recognizes merged.
Conflict handling: same auto-resolve as cherry-pick — entity-only conflicts
take main's version (--ours = current worktree HEAD = main), other conflicts
abort with detail.
Backout: config.EXTERNAL_PR_NO_FF_MERGE = True (default). Set False to fall
back to cherry-pick if no-ff destabilizes throughput one week pre-Accelerate.
Branch dispatch in _merge_domain_queue:
- reweave/* → _merge_reweave_pr (existing)
- gh-pr-N/* AND config.EXTERNAL_PR_NO_FF_MERGE → _merge_no_ff_external (new)
- everything else → _cherry_pick_onto_main (existing default)
Verified end-to-end in scratch repo:
- merge commit M has [main_sha, contributor_sha] as parents
- contributor SHA is ancestor of M
- after ff-push, contributor SHA is in main's history (GitHub badge fires)
- regex parses 8 cases correctly (real fork PR + edge cases reject cleanly)
Architecture per Ship Msg 3 / doc v3 (537cfd5 on epimetheus/external-merge-flow-design).
Phase 1 (sync-mirror self-heal) deployed yesterday. Phase 3 (FwazB PR #90 cleanup)
queued behind this deploy.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
parent
de204db539
commit
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2 changed files with 144 additions and 0 deletions
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@ -84,6 +84,14 @@ MAX_EXTRACT_WORKERS = int(os.environ.get("MAX_EXTRACT_WORKERS", "5"))
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MAX_EVAL_WORKERS = int(os.environ.get("MAX_EVAL_WORKERS", "7"))
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MAX_MERGE_WORKERS = 1 # domain-serialized, but one merge at a time per domain
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# --- External GitHub PR merge strategy ---
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# When True, gh-pr-N/* branches merge with --no-ff (preserves contributor SHA in
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# main's history → GitHub recognizes "merged" badge). When False, fall back to
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# cherry-pick (the default for all other branches). Default True; flip to False
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# as an emergency backout if the no-ff path destabilizes merge throughput.
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# Phase 2 of external contributor merge flow (Ship architecture review Apr 28).
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EXTERNAL_PR_NO_FF_MERGE = True
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# --- Timeouts (seconds) ---
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EXTRACT_TIMEOUT = 600 # 10 min
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EVAL_TIMEOUT = 120 # 2 min — routine Sonnet/Gemini Flash calls (was 600, caused 10-min stalls)
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136
lib/merge.py
136
lib/merge.py
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@ -429,6 +429,136 @@ async def _cherry_pick_onto_main(branch: str) -> tuple[bool, str]:
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await _git("branch", "-D", clean_branch)
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_GH_PR_BRANCH_RE = re.compile(r"^gh-pr-(\d+)/(.+)$")
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async def _merge_no_ff_external(branch: str) -> tuple[bool, str]:
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"""Merge an external GitHub fork PR with --no-ff so contributor SHA lands in main.
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Why this differs from _cherry_pick_onto_main:
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- Cherry-pick rewrites the contributor's commit SHA → GitHub's "is PR head SHA
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an ancestor of main?" check returns false → "merged" badge never fires.
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- --no-ff preserves the contributor's commit SHA as a parent of the merge
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commit. After ff-push to main (the existing dispatch step), GitHub sees
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the SHA in ancestry and marks the PR merged.
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Mechanics:
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1. Fetch origin/main + origin/{branch}
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2. Detached worktree at origin/main, git merge --no-ff origin/{branch}
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with verbose message: "Merge external GitHub PR #{N}: {branch_slug}"
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3. Force-push the merge commit as origin/{branch} (replacing the branch tip).
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Dispatch's existing ff-push to main then produces the merge commit on main.
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The merge commit M has parents [main_sha, branch_sha]. M is a fast-forward
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descendant of main_sha (via first-parent chain), so the ff-push to main
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works without --force.
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Conflict handling: same auto-resolve pattern as cherry-pick — entity-only
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conflicts take main's version (--ours = current worktree HEAD = main),
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other conflicts abort and return False with detail.
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Phase 2 of external contributor merge flow (Ship architecture review Apr 28).
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"""
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m = _GH_PR_BRANCH_RE.match(branch)
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if not m:
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return False, f"branch {branch} doesn't match gh-pr-N/* format"
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gh_pr_num = m.group(1)
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branch_slug = m.group(2)
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worktree_path = f"/tmp/teleo-merge-{branch.replace('/', '-')}"
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# Fetch latest state — separate calls (long branch names break combined refspec)
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rc, out = await _git("fetch", "origin", "main", timeout=15)
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if rc != 0:
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return False, f"fetch main failed: {out}"
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rc, out = await _git("fetch", "origin", branch, timeout=15)
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if rc != 0:
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return False, f"fetch branch failed: {out}"
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# Up-to-date check (mirrors cherry-pick path semantics)
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rc, merge_base = await _git("merge-base", "origin/main", f"origin/{branch}")
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rc2, main_sha = await _git("rev-parse", "origin/main")
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if rc == 0 and rc2 == 0 and merge_base.strip() == main_sha.strip():
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rc_diff, diff_out = await _git(
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"diff", "--stat", f"origin/main..origin/{branch}", timeout=10,
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)
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if rc_diff != 0 or not diff_out.strip():
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return True, "already up to date"
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logger.info("External PR branch %s is descendant of main but has new content — proceeding", branch)
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async with _bare_repo_lock:
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rc, out = await _git("worktree", "add", "--detach", worktree_path, "origin/main")
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if rc != 0:
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return False, f"worktree add failed: {out}"
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try:
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merge_msg = f"Merge external GitHub PR #{gh_pr_num}: {branch_slug}"
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rc, out = await _git(
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"merge", "--no-ff", f"origin/{branch}",
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"-m", merge_msg,
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cwd=worktree_path, timeout=60,
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)
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if rc != 0:
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# Identify conflicts
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rc_ls, conflicting = await _git(
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"diff", "--name-only", "--diff-filter=U", cwd=worktree_path,
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)
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conflict_files = [
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f.strip() for f in conflicting.split("\n") if f.strip()
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] if rc_ls == 0 else []
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if conflict_files and all(f.startswith("entities/") for f in conflict_files):
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# Entity-only conflicts: take main's version (entities are recoverable)
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# In merge: --ours = branch we're ON (worktree HEAD = main)
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# --theirs = branch merging in (origin/{branch})
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for cf in conflict_files:
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await _git("checkout", "--ours", cf, cwd=worktree_path)
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await _git("add", cf, cwd=worktree_path)
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# Complete the merge using the prepared MERGE_MSG (no editor)
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rc_cont, cont_out = await _git(
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"-c", "core.editor=true",
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"commit", "--no-edit",
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cwd=worktree_path, timeout=60,
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)
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if rc_cont != 0:
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await _git("merge", "--abort", cwd=worktree_path)
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return False, f"merge entity resolution failed for PR #{gh_pr_num}: {cont_out}"
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logger.info(
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"External PR #%s merge: entity conflict auto-resolved (dropped %s)",
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gh_pr_num, ", ".join(sorted(conflict_files)),
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)
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else:
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conflict_detail = ", ".join(conflict_files) if conflict_files else out[:200]
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await _git("merge", "--abort", cwd=worktree_path)
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return False, f"merge conflict on PR #{gh_pr_num}: {conflict_detail}"
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# Force-push the merge commit as origin/{branch}, replacing the contributor's
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# branch tip. Dispatch then ff-pushes origin/{branch} → main, producing the
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# merge commit on main. --force-with-lease guards against concurrent updates.
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rc, expected_sha = await _git("rev-parse", f"origin/{branch}")
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if rc != 0:
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return False, f"rev-parse origin/{branch} failed: {expected_sha}"
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expected_sha = expected_sha.strip().split("\n")[0]
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rc, out = await _git(
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"push",
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f"--force-with-lease={branch}:{expected_sha}",
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"origin",
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f"HEAD:{branch}",
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cwd=worktree_path,
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timeout=30,
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)
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if rc != 0:
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return False, f"push rejected: {out}"
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return True, f"merged --no-ff (external PR #{gh_pr_num})"
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finally:
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async with _bare_repo_lock:
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await _git("worktree", "remove", "--force", worktree_path)
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from .frontmatter import (
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REWEAVE_EDGE_FIELDS,
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parse_yaml_frontmatter,
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@ -733,6 +863,12 @@ async def _merge_domain_queue(conn, domain: str) -> tuple[int, int]:
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# (Ganymede: manifest approach, Theseus: superset assertion + order-preserving dedup)
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if branch.startswith("reweave/"):
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merge_fn = _merge_reweave_pr(branch)
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elif branch.startswith("gh-pr-") and config.EXTERNAL_PR_NO_FF_MERGE:
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# External GitHub fork PRs: --no-ff merge so contributor SHA lands
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# in main's history → GitHub recognizes "merged" badge.
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# Backout via config.EXTERNAL_PR_NO_FF_MERGE = False (falls back to cherry-pick).
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# Phase 2 of external contributor merge flow (Ship architecture review Apr 28).
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merge_fn = _merge_no_ff_external(branch)
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else:
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# Extraction commits ADD new files — cherry-pick applies cleanly.
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merge_fn = _cherry_pick_onto_main(branch)
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