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fix(engine): surface phantom-finalize cause and reset HEAD when branch is authoritative

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commitOrAmendMergeWithFixes used to swallow every unexpected throw as
`reason: "unknown-phantom"` and the two callers re-threw a bare
"verification fix finalize failed (unknown phantom)" with no operator-
actionable signal. FN-5422-class wedges (preAttemptHeadSha == currentHead
but branchTip ahead with task-trailered commits) couldn't be diagnosed
without re-running.

The catch now records the original error and probes whether the branch
ref itself is authoritative for the task (tip carries Fusion-Task-Id
trailer, base..branch is foreign-contamination-free). When it is — i.e.
the work isn't lost, the integration worktree just didn't advance — the
catch resets rootDir to preAttemptHeadSha so the next merge attempt
starts from a known baseline instead of inheriting partial squash state,
and returns `reason: "branch-ref-ahead-reset"`. The two callers fold
`originalError=` and `branchAuthority=` into the thrown message so the
real cause (diff-volume gate, file-scope, transient git, etc.) is
visible in the run log.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
gsxdsm
2026-05-21 19:10:24 -07:00
parent d947197c2a
commit a2a5db8151
2 changed files with 52 additions and 6 deletions
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49
packages/engine/src/merger.ts
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@@ -40,6 +40,7 @@ import {
filterFilesToOwnTaskCommits,
SilentNoOpAttributionMismatchError,
} from "./branch-attribution.js";
import { isBranchAuthoritativeForTask } from "./branch-conflicts.js";
import { hostname } from "node:os";
import {
buildTaskLineageTrailer,
@@ -3369,7 +3370,7 @@ type MergeFinalizeResult =
mergeSha?: string;
strategy?: AlreadyMergedDetectionStrategy;
}
| { ok: false; reason: "fix-produced-no-content" | "unknown-phantom" };
| { ok: false; reason: "fix-produced-no-content" | "unknown-phantom" | "branch-ref-ahead-reset"; originalError?: string; branchAuthority?: "ok" | string };
async function persistFinalizeResetLeftovers(rootDir: string, taskId: string, store?: TaskStore): Promise<void> {
try {
@@ -3963,7 +3964,35 @@ export async function commitOrAmendMergeWithFixes(
}
const errorMessage = err instanceof Error ? err.message : String(err);
mergerLog.warn(`${taskId}: failed to finalize merge commit: ${errorMessage}`);
return { ok: false, reason: "unknown-phantom" };
// FN-5422-class diagnostic: when finalize throws but the branch ref still
// carries this task's authoritative lineage (tip trailer + no foreign
// FN-attributed commits in base..branch), the work isn't lost — it's just
// that this attempt's integration worktree never advanced. Reset rootDir
// to preAttemptHeadSha so the next merge attempt starts clean, and tag
// the result so the caller's diagnostic includes that context.
const authority = await isBranchAuthoritativeForTask(rootDir, branch, taskId, preAttemptHeadSha).catch(
() => ({ ok: false as const, reason: "authority-probe-failed" }),
);
if (authority.ok) {
try {
await execAsync(`git reset --hard ${preAttemptHeadSha}`, { cwd: rootDir, encoding: "utf-8" });
await execAsync("git clean -fd", { cwd: rootDir, encoding: "utf-8" });
mergerLog.warn(
`${taskId}: finalize threw but branch ref is authoritative (tip carries Fusion-Task-Id, no foreign commits since base) — reset HEAD to ${preAttemptHeadSha.slice(0, 8)} for clean retry`,
);
} catch (resetErr: unknown) {
mergerLog.warn(
`${taskId}: branch-authoritative reset failed: ${resetErr instanceof Error ? resetErr.message : String(resetErr)}`,
);
}
return { ok: false, reason: "branch-ref-ahead-reset", originalError: errorMessage, branchAuthority: "ok" };
}
return {
ok: false,
reason: "unknown-phantom",
originalError: errorMessage,
branchAuthority: authority.ok ? "ok" : authority.reason,
};
}
}
@@ -8438,9 +8467,13 @@ export async function aiMergeTask(
resetMergeWithWarn(rootDir, taskId, "verification-fix finalize");
const classification = finalized.reason === "fix-produced-no-content"
? "fix produced no content"
: "unknown phantom";
: finalized.reason === "branch-ref-ahead-reset"
? "branch-ref ahead of integration target (reset for retry)"
: "unknown phantom";
const originalErrorSuffix = finalized.originalError ? ` originalError="${finalized.originalError}";` : "";
const authoritySuffix = finalized.branchAuthority ? ` branchAuthority=${finalized.branchAuthority};` : "";
throw new Error(
`${taskId}: verification fix finalize failed (${classification}); preAttemptHeadSha=${preAttemptHeadSha}; currentHead=${currentHeadOut.trim()}; branch=${branch}; branchTip=${branchTipOut.trim()}.`,
`${taskId}: verification fix finalize failed (${classification}); preAttemptHeadSha=${preAttemptHeadSha}; currentHead=${currentHeadOut.trim()}; branch=${branch}; branchTip=${branchTipOut.trim()};${originalErrorSuffix}${authoritySuffix}`,
);
}
return true; // Merge succeeds
@@ -8582,9 +8615,13 @@ export async function aiMergeTask(
resetMergeWithWarn(rootDir, taskId, "build-verification fix finalize");
const classification = finalized.reason === "fix-produced-no-content"
? "fix produced no content"
: "unknown phantom";
: finalized.reason === "branch-ref-ahead-reset"
? "branch-ref ahead of integration target (reset for retry)"
: "unknown phantom";
const originalErrorSuffix = finalized.originalError ? ` originalError="${finalized.originalError}";` : "";
const authoritySuffix = finalized.branchAuthority ? ` branchAuthority=${finalized.branchAuthority};` : "";
throw new Error(
`${taskId}: build verification fix finalize failed (${classification}); preAttemptHeadSha=${preAttemptHeadSha}; currentHead=${currentHeadOut.trim()}; branch=${branch}; branchTip=${branchTipOut.trim()}.`,
`${taskId}: build verification fix finalize failed (${classification}); preAttemptHeadSha=${preAttemptHeadSha}; currentHead=${currentHeadOut.trim()}; branch=${branch}; branchTip=${branchTipOut.trim()};${originalErrorSuffix}${authoritySuffix}`,
);
}
return true; // Merge succeeds