feat(FN-4545): complete Step 2 — add contamination auto-recovery handler

Fusion-Task-Id: FN-4545
Fusion-Task-Lineage: 95108429-618e-4a6d-9fa9-7ac2596665a2

packages/engine/src/auto-recovery-handlers/contamination.ts

@@ -0,0 +1,76 @@
+import type { TaskStore } from "@fusion/core";
+import type { AutoRecoveryContext, AutoRecoveryDecision, AutoRecoveryFailure, AutoRecoveryHandlers } from "../auto-recovery.js";
+import { createLogger, type Logger } from "../logger.js";
+import type { RunAuditor } from "../run-audit.js";
+
+const baseLog = createLogger("auto-recovery:contamination");
+
+export interface ContaminationRecoveryDeps {
+  taskStore: TaskStore;
+  runAudit: RunAuditor;
+  logger?: Logger;
+  repoDir: string;
+}
+
+export class ContaminationAutoRecoveryHandler implements Pick<AutoRecoveryHandlers, "issueRetry"> {
+  constructor(private readonly deps: ContaminationRecoveryDeps) {}
+
+  private get logger(): Logger {
+    return this.deps.logger ?? baseLog;
+  }
+
+  async issueRetry(failure: AutoRecoveryFailure, decision: AutoRecoveryDecision, ctx: AutoRecoveryContext): Promise<void> {
+    void this.deps.repoDir;
+    const task = ctx.task;
+    if (task.userPaused) {
+      this.logger.warn(`auto-recovery: skipped (userPaused) class=${failure.class} task=${task.id}`);
+      return;
+    }
+
+    const ownCommits = Number(failure.evidence?.ownCommits ?? 0);
+    const foreignAttributedCommits = Number(failure.evidence?.foreignAttributedCommits ?? 0);
+    const maxRetries = ctx.settings.maxRetries ?? 3;
+
+    if ((ownCommits > 0 && foreignAttributedCommits > 0) || ctx.retryCount >= maxRetries) {
+      this.logger.warn(`auto-recovery: irreducible contamination reached retry path class=${failure.class} task=${task.id}`);
+      await this.deps.runAudit.database({
+        type: "contamination:irreducible-pause",
+        target: task.id,
+        metadata: {
+          class: failure.class,
+          rationale: decision.rationale,
+          ownCommits,
+          foreignAttributedCommits,
+          retryCount: ctx.retryCount,
+          maxRetries,
+        },
+      });
+      return;
+    }
+
+    await this.deps.taskStore.moveTask(task.id, "todo", {
+      moveSource: "engine",
+      preserveResumeState: true,
+      preserveProgress: true,
+      preserveWorktree: true,
+    });
+
+    await this.deps.taskStore.updateTask(task.id, {
+      paused: false,
+      pausedReason: null,
+      error: null,
+    });
+
+    await this.deps.runAudit.database({
+      type: "contamination:retry-issued",
+      target: task.id,
+      metadata: {
+        class: failure.class,
+        rationale: decision.rationale,
+        ownCommits,
+        foreignAttributedCommits,
+        retryCount: ctx.retryCount,
+      },
+    });
+  }
+}