diff --git a/src/daemon/error-detector.ts b/src/daemon/error-detector.ts
index 0c36a9c..6059861 100644
--- a/src/daemon/error-detector.ts
+++ b/src/daemon/error-detector.ts
@@ -61,9 +61,25 @@ export interface CliError {
  * 5xx as transient). 4xx codes (401/402/403/429) are NOT retried;
  * they're either auth/quota or already rate-limited. Retrying 429
  * immediately would just compound the rate-limit.
+ *
+ * Lineage-specific extension (PR #85): when `kind` is undefined AND
+ * `lineage === 'opencode'`, treat as retryable. Opencode-go's gateway
+ * has known transport flakes where the subprocess exits 0 with empty
+ * output (no classified errorKind, no message) but a second attempt
+ * succeeds. Other lineages keep the conservative "no kind = not
+ * retryable" default — codex/claude/gemini's null-with-no-kind cases
+ * usually mean the model genuinely produced nothing, where retry would
+ * just produce nothing again. Victor caught the gap on the PR #83
+ * audit (qwen3.6-plus on opencode produced null, no retry, straight to
+ * claude fallback — wasted the cheap save).
  */
-export function isRetryableErrorKind(kind: string | undefined): boolean {
-  if (!kind) return false;
+export function isRetryableErrorKind(
+  kind: string | undefined,
+  lineage?: string,
+): boolean {
+  if (!kind) {
+    return lineage === 'opencode';
+  }
   switch (kind) {
     case 'cold_start_timeout':
     case 'tmux_dead':
diff --git a/src/daemon/runner/doer-driver.ts b/src/daemon/runner/doer-driver.ts
index 7de8f4a..7e96610 100644
--- a/src/daemon/runner/doer-driver.ts
+++ b/src/daemon/runner/doer-driver.ts
@@ -227,7 +227,7 @@ export async function runDoer(
             });
             if (result !== null) return result;
             if (attempt === MAX_ATTEMPTS) return null;
-            if (!isRetryableErrorKind(lastError.kind)) return null;
+            if (!isRetryableErrorKind(lastError.kind, entry.lineage)) return null;
             if (handle.signal.aborted) return null;
             console.warn(
               `[doer] retrying transient failure chat=${chatId} round=${round} ` +
diff --git a/src/daemon/runner/reviewer-driver.ts b/src/daemon/runner/reviewer-driver.ts
index eb54b76..1db6560 100644
--- a/src/daemon/runner/reviewer-driver.ts
+++ b/src/daemon/runner/reviewer-driver.ts
@@ -563,7 +563,7 @@ async function runReviewer(
               });
               if (result !== null) return result;
               if (attempt === MAX_ATTEMPTS) return null;
-              if (!isRetryableErrorKind(lastError.kind)) return null;
+              if (!isRetryableErrorKind(lastError.kind, entry.lineage)) return null;
               if (handle.signal.aborted) return null;
               console.warn(
                 `[reviewer] retrying transient failure chat=${chatId} round=${round} ` +
diff --git a/tests/error-detector-retryable.test.ts b/tests/error-detector-retryable.test.ts
index 50b9257..2c273cf 100644
--- a/tests/error-detector-retryable.test.ts
+++ b/tests/error-detector-retryable.test.ts
@@ -11,7 +11,7 @@ import { describe, expect, it } from 'vitest';
 import { isRetryableErrorKind } from '@/daemon/error-detector';
 
 describe('isRetryableErrorKind', () => {
-  it('returns false for undefined kind', () => {
+  it('returns false for undefined kind (no lineage)', () => {
     // Happy-path null result with no recorded errorSummary — no retry.
     expect(isRetryableErrorKind(undefined)).toBe(false);
   });
@@ -20,6 +20,34 @@ describe('isRetryableErrorKind', () => {
     expect(isRetryableErrorKind('')).toBe(false);
   });
 
+  describe('opencode-null special case (PR #85)', () => {
+    it('returns TRUE for undefined kind when lineage is opencode', () => {
+      // Opencode-go's gateway has known transport flakes where the
+      // subprocess exits 0 with empty output (no errorKind, no message)
+      // but a second attempt succeeds. Without this the qwen-style
+      // null-with-no-kind failure goes straight to fallback chain
+      // advance, wasting the cheap save.
+      expect(isRetryableErrorKind(undefined, 'opencode')).toBe(true);
+    });
+
+    it('keeps the conservative default for other lineages on undefined kind', () => {
+      // codex/claude/gemini null-with-no-kind usually means the model
+      // genuinely produced nothing — retry would produce nothing again.
+      expect(isRetryableErrorKind(undefined, 'openai')).toBe(false);
+      expect(isRetryableErrorKind(undefined, 'anthropic')).toBe(false);
+      expect(isRetryableErrorKind(undefined, 'google')).toBe(false);
+      expect(isRetryableErrorKind(undefined, 'antigravity')).toBe(false);
+    });
+
+    it('the lineage hint does NOT override an explicit non-retryable kind', () => {
+      // Even on opencode, an auth/quota/db-corrupt kind is still
+      // terminal — retry would just produce the same error.
+      expect(isRetryableErrorKind('quota_exhausted', 'opencode')).toBe(false);
+      expect(isRetryableErrorKind('opencode_db_corrupt', 'opencode')).toBe(false);
+      expect(isRetryableErrorKind('no_output', 'opencode')).toBe(false);
+    });
+  });
+
   describe('terminal kinds (never retry)', () => {
     it('quota_exhausted is terminal', () => {
       // Quota windows are server-scheduled; retry within the same