diff --git a/packages/claude-code-plugin/__tests__/rdpath-find-integration.test.ts b/packages/claude-code-plugin/__tests__/rdpath-find-integration.test.ts
index 3d084c9dd..fccb0736f 100644
--- a/packages/claude-code-plugin/__tests__/rdpath-find-integration.test.ts
+++ b/packages/claude-code-plugin/__tests__/rdpath-find-integration.test.ts
@@ -467,5 +467,76 @@ Active step.
       expect(normalizeOutputPath(result.stdout)).toMatch(/^\.work\/\d{4}-\d{2}-\d{2}-plan\.json$/);
       expect(result.stderr).not.toContain('Invalid id');
     });
+
+    it('soft-fails legacy session ownership format when RD_WORK_PATH is set', async () => {
+      // SessionService.loadSession throws 'Legacy session ownership format
+      // detected' when session.json contains 'ownedRunbooks' (or
+      // 'stashedRunbookOwnership'). isRecoverableActiveStateLookupError must
+      // recognize this so rdpath assembles a path without a context segment.
+      await fs.mkdir(path.join(testDir, '.rundown'), { recursive: true });
+      await fs.writeFile(
+        path.join(testDir, '.rundown', 'session.json'),
+        JSON.stringify({ ownedRunbooks: { 'wf-old-run': { runbookPath: 'foo.md' } } }, null, 2),
+      );
+
+      const result = await runRdpath(
+        ['--file', 'plan.json'],
+        {
+          RD_WORK_PATH: '.work',
+          RD_CONTEXT_ID: undefined,
+        },
+        testDir,
+      );
+
+      expect(result.exitCode).toBe(0);
+      expect(normalizeOutputPath(result.stdout)).toMatch(/^\.work\/\d{4}-\d{2}-\d{2}-plan\.json$/);
+      expect(result.stderr).toBe('');
+    });
+
+    it('soft-fails legacy stacks session format when RD_WORK_PATH is set', async () => {
+      // Second variant of the legacy ownership branch: 'stacks' key triggers
+      // the same recoverable error path.
+      await fs.mkdir(path.join(testDir, '.rundown'), { recursive: true });
+      await fs.writeFile(
+        path.join(testDir, '.rundown', 'session.json'),
+        JSON.stringify({ stacks: { default: [] } }, null, 2),
+      );
+
+      const result = await runRdpath(
+        ['--file', 'plan.json'],
+        {
+          RD_WORK_PATH: '.work',
+          RD_CONTEXT_ID: undefined,
+        },
+        testDir,
+      );
+
+      expect(result.exitCode).toBe(0);
+      expect(normalizeOutputPath(result.stdout)).toMatch(/^\.work\/\d{4}-\d{2}-\d{2}-plan\.json$/);
+      expect(result.stderr).toBe('');
+    });
+
+    it('soft-fails session.json that fails schema validation when RD_WORK_PATH is set', async () => {
+      // 'Session file contains invalid runbook targeting data' is thrown when
+      // session.json parses as JSON but fails SessionDataSchema validation.
+      await fs.mkdir(path.join(testDir, '.rundown'), { recursive: true });
+      await fs.writeFile(
+        path.join(testDir, '.rundown', 'session.json'),
+        JSON.stringify({ defaultStack: [{ not: 'a-string' }] }, null, 2),
+      );
+
+      const result = await runRdpath(
+        ['--file', 'plan.json'],
+        {
+          RD_WORK_PATH: '.work',
+          RD_CONTEXT_ID: undefined,
+        },
+        testDir,
+      );
+
+      expect(result.exitCode).toBe(0);
+      expect(normalizeOutputPath(result.stdout)).toMatch(/^\.work\/\d{4}-\d{2}-\d{2}-plan\.json$/);
+      expect(result.stderr).toBe('');
+    });
   });
 });
diff --git a/packages/core/__tests__/runbook/run-id.test.ts b/packages/core/__tests__/runbook/run-id.test.ts
new file mode 100644
index 000000000..0c6e7c03a
--- /dev/null
+++ b/packages/core/__tests__/runbook/run-id.test.ts
@@ -0,0 +1,120 @@
+import { describe, it, expect } from '@jest/globals';
+import { RUN_ID_PATTERN, RUN_ID_PREFIX, assertRunId, isRunId } from '../../src/runbook/run-id.js';
+
+describe('isRunId', () => {
+  it('accepts canonical rd_ + 32 lowercase hex chars', () => {
+    expect(isRunId('rd_4b7f0c2d9e1a4b7f0c2d9e1a4b7f0c2d')).toBe(true);
+  });
+
+  it('accepts all-zero hex segment', () => {
+    expect(isRunId('rd_00000000000000000000000000000000')).toBe(true);
+  });
+
+  it('accepts all-f hex segment', () => {
+    expect(isRunId('rd_ffffffffffffffffffffffffffffffff')).toBe(true);
+  });
+
+  it('rejects uppercase hex characters', () => {
+    expect(isRunId('rd_ABCDEF00000000000000000000000000')).toBe(false);
+  });
+
+  it('rejects uppercase RD_ prefix', () => {
+    expect(isRunId('RD_00000000000000000000000000000000')).toBe(false);
+  });
+
+  it('rejects missing prefix', () => {
+    expect(isRunId('00000000000000000000000000000000')).toBe(false);
+  });
+
+  it('rejects 31-char hex segment', () => {
+    expect(isRunId('rd_0000000000000000000000000000000')).toBe(false);
+  });
+
+  it('rejects 33-char hex segment', () => {
+    expect(isRunId('rd_000000000000000000000000000000000')).toBe(false);
+  });
+
+  it('rejects non-hex character in segment', () => {
+    expect(isRunId('rd_g0000000000000000000000000000000')).toBe(false);
+  });
+
+  it('rejects hyphenated UUID-style body', () => {
+    expect(isRunId('rd_550e8400-e29b-41d4-a716-446655440000')).toBe(false);
+  });
+
+  it('rejects empty string', () => {
+    expect(isRunId('')).toBe(false);
+  });
+
+  it('rejects bare prefix with no body', () => {
+    expect(isRunId('rd_')).toBe(false);
+  });
+
+  it('rejects legacy wf-YYYY-MM-DD-... format', () => {
+    expect(isRunId('wf-2024-01-07-abc123')).toBe(false);
+  });
+
+  it('rejects non-string values', () => {
+    expect(isRunId(undefined)).toBe(false);
+    expect(isRunId(null)).toBe(false);
+    expect(isRunId(123)).toBe(false);
+    expect(isRunId({})).toBe(false);
+  });
+});
+
+describe('assertRunId', () => {
+  it('returns the input when valid', () => {
+    const raw = 'rd_4b7f0c2d9e1a4b7f0c2d9e1a4b7f0c2d';
+    expect(assertRunId(raw)).toBe(raw);
+  });
+
+  it('throws on invalid id with a message naming the expected format', () => {
+    expect(() => assertRunId('not-a-run-id')).toThrow(/rd_/);
+  });
+
+  it('throws on uppercase hex', () => {
+    expect(() => assertRunId('rd_ABCDEF00000000000000000000000000')).toThrow();
+  });
+
+  it('throws on empty string', () => {
+    expect(() => assertRunId('')).toThrow();
+  });
+
+  it('throws on bare prefix', () => {
+    expect(() => assertRunId('rd_')).toThrow();
+  });
+
+  it('is idempotent for valid ids', () => {
+    const raw = 'rd_22222222222222222222222222222222';
+    expect(assertRunId(assertRunId(raw))).toBe(raw);
+  });
+});
+
+describe('RUN_ID_PATTERN / RUN_ID_PREFIX', () => {
+  it('exports the rd_ prefix constant', () => {
+    expect(RUN_ID_PREFIX).toBe('rd_');
+  });
+
+  it('exposes a pattern that anchors both ends', () => {
+    expect(RUN_ID_PATTERN.source.startsWith('^')).toBe(true);
+    expect(RUN_ID_PATTERN.source.endsWith('$')).toBe(true);
+  });
+
+  it('matches values accepted by isRunId', () => {
+    const id = 'rd_11111111111111111111111111111111';
+    expect(RUN_ID_PATTERN.test(id)).toBe(true);
+    expect(isRunId(id)).toBe(true);
+  });
+
+  it.each([
+    ['missing rd_ prefix', '00000000000000000000000000000000'],
+    ['uppercase hex', 'rd_ABCDEF00000000000000000000000000'],
+    ['31-char body (too short)', 'rd_0000000000000000000000000000000'],
+    ['33-char body (too long)', 'rd_000000000000000000000000000000000'],
+    ['non-hex character in body', 'rd_g0000000000000000000000000000000'],
+    ['hyphenated UUID body', 'rd_550e8400-e29b-41d4-a716-446655440000'],
+  ])('rejects %s in both RUN_ID_PATTERN and isRunId', (_label, value) => {
+    expect(RUN_ID_PATTERN.test(value)).toBe(false);
+    expect(isRunId(value)).toBe(false);
+  });
+});