diff --git a/packages/loopover-miner/lib/attempt-cli.ts b/packages/loopover-miner/lib/attempt-cli.ts
index 643af871fa..f880cb99d6 100644
--- a/packages/loopover-miner/lib/attempt-cli.ts
+++ b/packages/loopover-miner/lib/attempt-cli.ts
@@ -43,7 +43,7 @@ import type { GovernorLedger } from "./governor-ledger.js";
 import { openWorktreeAllocator } from "./worktree-allocator.js";
 import type { WorktreeAllocation, WorktreeAllocator } from "./worktree-allocator.js";
 import { isValidRepoSegment } from "./repo-clone.js";
-import { REJECTION_REASON_AI_USAGE_POLICY_BAN, REJECTION_REASON_OWN_SUBMISSION_REJECTED, resolveRejectionSignaled } from "./rejection-signal.js";
+import { REJECTION_REASON_AI_USAGE_POLICY_BAN, REJECTION_REASON_OWN_SUBMISSION_REJECTED, resolveOwnOpenPrForIssue, resolveRejectionSignaled } from "./rejection-signal.js";
 import type { resolveRejectionSignaled as ResolveRejectionSignaledFn } from "./rejection-signal.js";
 import { cleanupAttemptWorktree, prepareAttemptWorktree } from "./attempt-worktree.js";
 import type {
@@ -141,6 +141,8 @@ export type RunAttemptOptions = {
   initSignalTrackingStore?: () => SignalStore;
   buildAttemptDeps?: typeof buildAttemptDeps;
   resolveRejectionSignaled?: typeof ResolveRejectionSignaledFn;
+  // #8808: injection seam for the own-open-PR idempotency guard, mirroring resolveRejectionSignaled above.
+  resolveOwnOpenPrForIssue?: typeof resolveOwnOpenPrForIssue;
   fetchImpl?: SelfReviewContextFetch;
   prepareAttemptWorktree?: typeof PrepareAttemptWorktreeFn;
   cleanupAttemptWorktree?: typeof CleanupAttemptWorktreeFn;
@@ -450,6 +452,51 @@ export async function runAttempt(args: string[], options: RunAttemptOptions = {}
       return 5;
     }
 
+    // #8808: idempotency against this miner's OWN already-open PR for this exact issue — the crash-retry
+    // double-open guard. Checked before a worktree slot is consumed, mirroring the rejection-signal block
+    // above. Fail-open by construction (resolveOwnOpenPrForIssue returns null on any read/fetch failure), so
+    // a hiccup never blocks a legitimate attempt; refusing (not adopting) is the safe disposition — the
+    // still-open PR is already doing this issue's job.
+    const ownOpenPr = await (options.resolveOwnOpenPrForIssue ?? resolveOwnOpenPrForIssue)(parsed.repoFullName, parsed.issueNumber, {
+      fetchImpl: options.fetchImpl,
+    } as Parameters<typeof resolveOwnOpenPrForIssue>[2]);
+    if (ownOpenPr !== null) {
+      const reason = "own_open_pr_for_issue";
+      attemptLog.appendAttemptLogEvent({
+        eventType: "attempt_aborted",
+        attemptId,
+        actionClass: "open_pr",
+        mode,
+        reason,
+        payload: { repoFullName: parsed.repoFullName, issueNumber: parsed.issueNumber, existingPullRequestNumber: ownOpenPr },
+      });
+      eventLedger.appendEvent({
+        type: "attempt_blocked",
+        repoFullName: parsed.repoFullName,
+        payload: { issueNumber: parsed.issueNumber, reason, existingPullRequestNumber: ownOpenPr },
+      });
+      const duplicateResult = {
+        outcome: "blocked_own_open_pr",
+        reason,
+        repoFullName: parsed.repoFullName,
+        issueNumber: parsed.issueNumber,
+        existingPullRequestNumber: ownOpenPr,
+        minerLogin: parsed.minerLogin,
+        base: parsed.base,
+        mode,
+        attemptId,
+      };
+      if (parsed.json) {
+        console.log(JSON.stringify(duplicateResult, null, 2));
+      } else {
+        console.error(
+          `Attempt for ${parsed.repoFullName}#${parsed.issueNumber} is blocked: this miner already has open PR #${ownOpenPr} for this issue (a crash-retry duplicate would double-open). Close it or wait for its outcome first.`,
+        );
+      }
+      options.onResult?.(duplicateResult as AttemptCliResult);
+      return 5;
+    }
+
     allocation = allocator.acquire(attemptId, parsed.repoFullName);
 
     // #7858: only when the operator has configured Neon (dbForkConfig !== null) -- otherwise a complete
diff --git a/packages/loopover-miner/lib/rejection-signal.ts b/packages/loopover-miner/lib/rejection-signal.ts
index b6d52ad3c6..18363e0878 100644
--- a/packages/loopover-miner/lib/rejection-signal.ts
+++ b/packages/loopover-miner/lib/rejection-signal.ts
@@ -49,7 +49,7 @@ export type RejectionSignalFetch = (
 
 type RejectionSignalResponse = Awaited<ReturnType<RejectionSignalFetch>>;
 
-type OwnRejectionHistorySubmission = { pullRequestNumber?: number | null | undefined };
+type OwnRejectionHistorySubmission = { pullRequestNumber?: number | null | undefined; issueNumber?: number | null | undefined };
 
 type ListOwnSubmissions = (filter: { repoFullName?: string }) => OwnRejectionHistorySubmission[];
 
@@ -152,11 +152,13 @@ async function fetchPullRequestPayload(
  * fetch/parse failure is skipped so it never blocks the others. Consumes both upstream modules without modifying
  * either. Every dependency is injectable for testing.
  */
-export async function resolveOwnRejectionHistory(repoFullName: string, options: OwnRejectionHistoryOptions = {}): Promise<boolean> {
-  const target = parseRepoFullName(repoFullName);
-  if (!target) return false;
-  const listSubmissions = options.listSubmissions ?? listRecentOwnSubmissions;
-  const resolved = {
+function resolveHistoryOptions(options: OwnRejectionHistoryOptions): {
+  fetchImpl: RejectionSignalFetch;
+  githubToken: string;
+  githubApiBaseUrl: string;
+  maxChecks: number;
+} {
+  return {
     fetchImpl: options.fetchImpl ?? (fetch as unknown as RejectionSignalFetch),
     githubToken: typeof options.githubToken === "string" ? options.githubToken.trim() : (process.env.GITHUB_TOKEN ?? ""),
     githubApiBaseUrl:
@@ -166,6 +168,13 @@ export async function resolveOwnRejectionHistory(repoFullName: string, options:
         ? (options.maxRejectionHistoryChecks as number)
         : DEFAULT_MAX_REJECTION_HISTORY_CHECKS,
   };
+}
+
+export async function resolveOwnRejectionHistory(repoFullName: string, options: OwnRejectionHistoryOptions = {}): Promise<boolean> {
+  const target = parseRepoFullName(repoFullName);
+  if (!target) return false;
+  const listSubmissions = options.listSubmissions ?? listRecentOwnSubmissions;
+  const resolved = resolveHistoryOptions(options);
 
   let submissions: OwnRejectionHistorySubmission[];
   try {
@@ -193,6 +202,52 @@ export async function resolveOwnRejectionHistory(repoFullName: string, options:
   return false;
 }
 
+/**
+ * #8808: does THIS miner already have an OPEN PR for THIS exact issue on THIS repo? The crash-retry
+ * double-open guard: claim-conflict resolution deliberately never treats the miner's own sibling PR as a
+ * competing claim, and freshness excludes same-author PRs -- so nothing downstream refuses a duplicate
+ * attempt. Reads the miner's own recorded submissions (issue-tagged since #8172-era rows), live-checks the
+ * most recent candidates' PR state (bounded by the same maxRejectionHistoryChecks fan-out cap), and returns
+ * the first still-OPEN PR number -- or null. FULLY FAIL-OPEN: any read/fetch failure returns null (an
+ * idempotency guard must never block a legitimate attempt on a hiccup; submission-freshness + the claim
+ * ledger remain the downstream backstops).
+ */
+export async function resolveOwnOpenPrForIssue(
+  repoFullName: string,
+  issueNumber: number,
+  options: OwnRejectionHistoryOptions = {},
+): Promise<number | null> {
+  const target = parseRepoFullName(repoFullName);
+  if (!target || !Number.isInteger(issueNumber) || issueNumber <= 0) return null;
+  const listSubmissions = options.listSubmissions ?? listRecentOwnSubmissions;
+  const resolved = resolveHistoryOptions(options);
+
+  let submissions: OwnRejectionHistorySubmission[];
+  try {
+    submissions = listSubmissions({ repoFullName });
+  } catch {
+    return null; // wholesale read failure -- fail open, never block an attempt on it
+  }
+  const candidates = (Array.isArray(submissions) ? submissions : [])
+    .filter(
+      (submission) =>
+        submission &&
+        submission.issueNumber === issueNumber &&
+        Number.isInteger(submission.pullRequestNumber) &&
+        (submission.pullRequestNumber as number) > 0,
+    )
+    .slice(0, resolved.maxChecks);
+  for (const candidate of candidates) {
+    try {
+      const payload = (await fetchPullRequestPayload(target, candidate.pullRequestNumber as number, resolved)) as { state?: unknown } | null;
+      if (payload && payload.state === "open") return candidate.pullRequestNumber as number;
+    } catch {
+      // Individual fetch failure -- skip (fail open), keep checking the rest.
+    }
+  }
+  return null;
+}
+
 /**
  * Resolve whether the target repo has signaled it does not want automated/AI-authored contributions --
  * either trigger documented above. Returns `false` (never throws) on any fetch/parse failure for the policy
diff --git a/test/unit/miner-attempt-cli.test.ts b/test/unit/miner-attempt-cli.test.ts
index 97bc0cd399..526de20e71 100644
--- a/test/unit/miner-attempt-cli.test.ts
+++ b/test/unit/miner-attempt-cli.test.ts
@@ -1571,6 +1571,70 @@ describe("runAttempt (#5132)", () => {
     expect(error).toHaveBeenCalledWith(expect.stringContaining("AI-usage policy bans automated/AI-authored contributions"));
   });
 
+  it("#8808: refuses a duplicate attempt when this miner already has an open PR for the exact issue (crash-retry double-open guard)", async () => {
+    const { allocator, claimLedger, eventLedger, attemptLog, governorLedger } = tempLedgers();
+    const log = vi.spyOn(console, "log").mockImplementation(() => undefined);
+    const appendAttemptLogEventSpy = vi.spyOn(attemptLog, "appendAttemptLogEvent");
+    const acquireSpy = vi.spyOn(allocator, "acquire");
+
+    const exitCode = await runAttempt(["acme/widgets", "7", "--miner-login", "alice", "--json"], {
+      env: { MINER_CODING_AGENT_PROVIDER: "noop" },
+      openWorktreeAllocator: () => allocator,
+      openClaimLedger: () => claimLedger,
+      initEventLedger: () => eventLedger,
+      initAttemptLog: () => attemptLog,
+      initGovernorLedger: () => governorLedger,
+      resolveRejectionSignaled: async () => false,
+      resolveOwnOpenPrForIssue: async () => 42,
+    });
+
+    expect(exitCode).toBe(5);
+    expect(acquireSpy).not.toHaveBeenCalled(); // refused BEFORE consuming a worktree slot
+    expect(appendAttemptLogEventSpy).toHaveBeenCalledWith(
+      expect.objectContaining({ eventType: "attempt_aborted", reason: "own_open_pr_for_issue" }),
+    );
+    const payload = JSON.parse(String(log.mock.calls.at(-1)?.[0]));
+    expect(payload).toMatchObject({ outcome: "blocked_own_open_pr", reason: "own_open_pr_for_issue", existingPullRequestNumber: 42 });
+  });
+
+  it("#8808: the non-json refusal names the existing PR on stderr", async () => {
+    const { allocator, claimLedger, eventLedger, attemptLog, governorLedger } = tempLedgers();
+    const error = vi.spyOn(console, "error").mockImplementation(() => undefined);
+
+    const exitCode = await runAttempt(["acme/widgets", "7", "--miner-login", "alice"], {
+      env: { MINER_CODING_AGENT_PROVIDER: "noop" },
+      openWorktreeAllocator: () => allocator,
+      openClaimLedger: () => claimLedger,
+      initEventLedger: () => eventLedger,
+      initAttemptLog: () => attemptLog,
+      initGovernorLedger: () => governorLedger,
+      resolveRejectionSignaled: async () => false,
+      resolveOwnOpenPrForIssue: async () => 42,
+    });
+
+    expect(exitCode).toBe(5);
+    expect(error).toHaveBeenCalledWith(expect.stringContaining("already has open PR #42"));
+  });
+
+  it("#8808: a null resolution (no open PR / fail-open hiccup) proceeds to the worktree slot exactly as before", async () => {
+    const { allocator, claimLedger, eventLedger, attemptLog, governorLedger } = tempLedgers();
+    vi.spyOn(console, "log").mockImplementation(() => undefined);
+    const acquireSpy = vi.spyOn(allocator, "acquire");
+
+    await runAttempt(["acme/widgets", "7", "--miner-login", "alice", "--json"], {
+      env: { MINER_CODING_AGENT_PROVIDER: "noop" },
+      openWorktreeAllocator: () => allocator,
+      openClaimLedger: () => claimLedger,
+      initEventLedger: () => eventLedger,
+      initAttemptLog: () => attemptLog,
+      initGovernorLedger: () => governorLedger,
+      resolveRejectionSignaled: async () => false,
+      resolveOwnOpenPrForIssue: async () => null,
+    });
+
+    expect(acquireSpy).toHaveBeenCalled(); // the guard let the attempt through
+  });
+
   it("REGRESSION (#6055): labels own-rejection-history aborts as own_submission_rejected in --json output", async () => {
     const { allocator, claimLedger, eventLedger, attemptLog, governorLedger } = tempLedgers();
     const log = vi.spyOn(console, "log").mockImplementation(() => undefined);
diff --git a/test/unit/miner-rejection-signal.test.ts b/test/unit/miner-rejection-signal.test.ts
index aff1e69c42..07bc4f575b 100644
--- a/test/unit/miner-rejection-signal.test.ts
+++ b/test/unit/miner-rejection-signal.test.ts
@@ -7,6 +7,7 @@ vi.mock("@loopover/engine", async () => {
 import {
   REJECTION_REASON_AI_USAGE_POLICY_BAN,
   REJECTION_REASON_OWN_SUBMISSION_REJECTED,
+  resolveOwnOpenPrForIssue,
   resolveOwnRejectionHistory,
   resolveRejectionSignaled,
 } from "../../packages/loopover-miner/lib/rejection-signal.js";
@@ -463,3 +464,64 @@ describe("resolveRejectionSignaled combines both triggers (#5655)", () => {
     expect(result).toBe(false);
   });
 });
+
+describe("resolveOwnOpenPrForIssue (#8808)", () => {
+  it("returns the still-open PR number when this miner already has one for the exact issue", async () => {
+    const fetchImpl = vi.fn(async (_url: string, _init?: unknown) => jsonResponse({ state: "open" }));
+    const result = await resolveOwnOpenPrForIssue("acme/widgets", 12, {
+      listSubmissions: () => [{ pullRequestNumber: 42, issueNumber: 12 }],
+      fetchImpl,
+    });
+    expect(result).toBe(42);
+    expect(String(fetchImpl.mock.calls[0]?.[0])).toContain("/repos/acme/widgets/pulls/42");
+  });
+
+  it("returns null (no fetch) when no recorded submission matches the issue — other issues' PRs never block", async () => {
+    const fetchImpl = vi.fn();
+    const result = await resolveOwnOpenPrForIssue("acme/widgets", 12, {
+      listSubmissions: () => [{ pullRequestNumber: 41, issueNumber: 11 }, { pullRequestNumber: null, issueNumber: 12 }, {}],
+      fetchImpl,
+    });
+    expect(result).toBeNull();
+    expect(fetchImpl).not.toHaveBeenCalled();
+  });
+
+  it("a CLOSED/merged prior PR for the issue does not block a fresh attempt", async () => {
+    const fetchImpl = vi.fn(async () => jsonResponse({ state: "closed" }));
+    const result = await resolveOwnOpenPrForIssue("acme/widgets", 12, {
+      listSubmissions: () => [{ pullRequestNumber: 42, issueNumber: 12 }],
+      fetchImpl,
+    });
+    expect(result).toBeNull();
+  });
+
+  it("FAIL-OPEN: a submissions read failure or a fetch rejection returns null — never blocks an attempt on a hiccup", async () => {
+    expect(
+      await resolveOwnOpenPrForIssue("acme/widgets", 12, {
+        listSubmissions: () => {
+          throw new Error("store down");
+        },
+        fetchImpl: vi.fn(),
+      }),
+    ).toBeNull();
+    expect(
+      await resolveOwnOpenPrForIssue("acme/widgets", 12, {
+        listSubmissions: () => [{ pullRequestNumber: 42, issueNumber: 12 }],
+        fetchImpl: vi.fn(async () => {
+          throw new Error("network");
+        }),
+      }),
+    ).toBeNull();
+  });
+
+  it("bounds the live checks to maxRejectionHistoryChecks and rejects degenerate inputs", async () => {
+    const fetchImpl = vi.fn(async () => jsonResponse({ state: "closed" }));
+    const submissions = Array.from({ length: 15 }, (_, i) => ({ pullRequestNumber: i + 1, issueNumber: 12 }));
+    expect(await resolveOwnOpenPrForIssue("acme/widgets", 12, { listSubmissions: () => submissions, fetchImpl, maxRejectionHistoryChecks: 3 })).toBeNull();
+    expect(fetchImpl).toHaveBeenCalledTimes(3);
+    expect(await resolveOwnOpenPrForIssue("not-a-repo", 12, { listSubmissions: () => submissions, fetchImpl })).toBeNull();
+    expect(await resolveOwnOpenPrForIssue("acme/widgets", 0, { listSubmissions: () => submissions, fetchImpl })).toBeNull();
+    // Defensive non-array return (mirrors the sibling resolver's own guard).
+    expect(await resolveOwnOpenPrForIssue("acme/widgets", 12, { listSubmissions: (() => null) as never, fetchImpl })).toBeNull();
+  });
+});