fix(attachments): harden document preview/thumbnail path (review of #120)

Follow-up hardening applied during review of PR #120, addressing the
adversarial multi-agent findings:

- fix(preview): render auto-detected (workspace, unregistered) DOCX/PPTX via
  the file-preview route and PDFs via file-raw in openFilePreview. Previously
  the Preview button fell through to file-content, dumping the binary Office/PDF
  bytes as mojibake, and the new file-preview route was unreachable dead code.
  (MAJOR: file-preview-route-unreachable-detected-office)

- perf(convert): add a global converter-concurrency limiter
  (document-conversion-limiter.ts) wrapping every pdftoppm / soffice /
  powershell spawn, so N simultaneous preview/thumbnail requests can no longer
  fork unbounded converter processes. Default cap 3, CODEMAN_MAX_DOCUMENT_CONVERSIONS.
  (MAJOR: no-converter-concurrency-limit)

- fix(cache): bound the converted-PDF disk cache with LRU-by-mtime eviction
  (pruneDocumentPreviewCache, default 100 files, CODEMAN_MAX_PREVIEW_CACHE_FILES),
  run after each successful conversion. Was unbounded.
  (MAJOR/MINOR: preview-cache-unbounded-disk-growth)

Tests: document-conversion-limiter.test.ts, document-preview-cache-eviction.test.ts,
and route coverage for the four new endpoints in
routes/file-routes-preview-thumbnail.test.ts (closes the missing-route-test gap).
Verified end-to-end against real pdftoppm (thumbnail render + concurrency cap).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/document-conversion-limiter.test.ts

@@ -0,0 +1,47 @@
+import { describe, it, expect } from 'vitest';
+import { runWithConversionLimit, getActiveConversionCount } from '../src/document-conversion-limiter.js';
+
+describe('document-conversion-limiter', () => {
+  it('never runs more converters than the cap (default 3) concurrently', async () => {
+    let running = 0;
+    let maxObserved = 0;
+
+    const task = () => async () => {
+      running++;
+      maxObserved = Math.max(maxObserved, running);
+      // The module's own accounting must also stay within the cap.
+      expect(getActiveConversionCount()).toBeLessThanOrEqual(3);
+      await new Promise((resolve) => setTimeout(resolve, 5));
+      running--;
+    };
+
+    await Promise.all(Array.from({ length: 12 }, () => runWithConversionLimit(task())));
+
+    expect(maxObserved).toBeLessThanOrEqual(3);
+    expect(maxObserved).toBeGreaterThan(1); // proves it genuinely parallelizes, not serializes
+    expect(getActiveConversionCount()).toBe(0); // every slot released
+  });
+
+  it('processes every queued task even when far more are submitted than the cap', async () => {
+    let completed = 0;
+    await Promise.all(
+      Array.from({ length: 25 }, () =>
+        runWithConversionLimit(async () => {
+          await new Promise((resolve) => setTimeout(resolve, 1));
+          completed++;
+        })
+      )
+    );
+    expect(completed).toBe(25);
+    expect(getActiveConversionCount()).toBe(0);
+  });
+
+  it('releases the slot when a task throws', async () => {
+    await expect(
+      runWithConversionLimit(async () => {
+        throw new Error('boom');
+      })
+    ).rejects.toThrow('boom');
+    expect(getActiveConversionCount()).toBe(0);
+  });
+});

test/document-preview-cache-eviction.test.ts

@@ -0,0 +1,55 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import fs from 'node:fs/promises';
+import { pruneDocumentPreviewCache } from '../src/document-preview-cache.js';
+
+vi.mock('node:fs/promises', () => ({
+  default: {
+    readdir: vi.fn(),
+    stat: vi.fn(),
+    rm: vi.fn(async () => undefined),
+  },
+}));
+
+const mockedReaddir = vi.mocked(fs.readdir);
+const mockedStat = vi.mocked(fs.stat);
+const mockedRm = vi.mocked(fs.rm);
+
+describe('pruneDocumentPreviewCache', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    // mtime encoded in the filename (f0 oldest ... f101 newest)
+    mockedStat.mockImplementation(async (p) => {
+      const m = /f(\d+)\.pdf$/.exec(String(p));
+      return { mtimeMs: m ? Number(m[1]) : 0, isFile: () => true } as never;
+    });
+  });
+
+  it('evicts the oldest *.pdf files once the cache exceeds the cap (default 100)', async () => {
+    const names = Array.from({ length: 102 }, (_, i) => `f${i}.pdf`);
+    mockedReaddir.mockResolvedValue(names as never);
+
+    await pruneDocumentPreviewCache('/tmp/codeman-document-preview-cache');
+
+    // 102 - 100 = 2 oldest removed
+    expect(mockedRm).toHaveBeenCalledTimes(2);
+    const removed = mockedRm.mock.calls.map((c) => String(c[0]));
+    expect(removed.some((p) => p.endsWith('f0.pdf'))).toBe(true);
+    expect(removed.some((p) => p.endsWith('f1.pdf'))).toBe(true);
+    expect(removed.some((p) => p.endsWith('f101.pdf'))).toBe(false); // newest kept
+  });
+
+  it('ignores non-pdf entries (e.g. transient work-* dirs) when counting', async () => {
+    const names = [...Array.from({ length: 50 }, (_, i) => `f${i}.pdf`), 'work-abc', 'work-def'];
+    mockedReaddir.mockResolvedValue(names as never);
+
+    await pruneDocumentPreviewCache('/tmp/codeman-document-preview-cache');
+
+    expect(mockedRm).not.toHaveBeenCalled(); // 50 pdfs <= cap
+  });
+
+  it('never throws when the cache dir cannot be read', async () => {
+    mockedReaddir.mockRejectedValue(new Error('ENOENT'));
+    await expect(pruneDocumentPreviewCache('/tmp/missing')).resolves.toBeUndefined();
+    expect(mockedRm).not.toHaveBeenCalled();
+  });
+});

test/routes/file-routes-preview-thumbnail.test.ts

@@ -0,0 +1,156 @@
+/**
+ * @fileoverview Route coverage for the document preview/thumbnail endpoints
+ * added in COD-38 (PR #120): the by-attachmentId routes
+ * (/attachments/:id/preview|thumbnail) and the workspace-path routes
+ * (/file-preview|/file-thumbnail). Converters are mocked, so no real
+ * pdftoppm/LibreOffice is needed. Uses app.inject() — no real ports.
+ */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { createRouteTestHarness, type RouteTestHarness } from './_route-test-utils.js';
+import { registerFileRoutes } from '../../src/web/routes/file-routes.js';
+
+vi.mock('node:fs/promises', () => ({
+  default: {
+    readFile: vi.fn(async () => Buffer.from('%PDF-1.4 fake pdf bytes')),
+    stat: vi.fn(async () => ({ size: 100, isFile: () => true, mtimeMs: 1 })),
+    readdir: vi.fn(async () => []),
+    mkdir: vi.fn(async () => undefined),
+    mkdtemp: vi.fn(async () => '/tmp/codeman-preview-test'),
+    rename: vi.fn(async () => undefined),
+    rm: vi.fn(async () => undefined),
+  },
+}));
+
+vi.mock('node:fs', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('node:fs')>();
+  return { ...actual, realpathSync: vi.fn((p: string) => p) };
+});
+
+// Mock the converters so the routes don't shell out to real binaries.
+vi.mock('../../src/document-thumbnailer.js', () => ({
+  generateFirstPageThumbnail: vi.fn(async () => ({ content: Buffer.from('\x89PNG fake'), contentType: 'image/png' })),
+}));
+vi.mock('../../src/document-preview-cache.js', () => ({
+  getOfficePreviewPdfPath: vi.fn(async () => '/tmp/codeman-document-preview-cache/out.pdf'),
+  getPreviewPdfDownloadName: vi.fn((name: string) => `${name.replace(/\.[^.]+$/, '')}.pdf`),
+}));
+
+import { generateFirstPageThumbnail } from '../../src/document-thumbnailer.js';
+import { getOfficePreviewPdfPath } from '../../src/document-preview-cache.js';
+import { attachmentRegistry, type AttachmentRecord } from '../../src/attachment-registry.js';
+
+const SID = 'test-session-1';
+const WORKDIR = '/tmp/test-workdir';
+
+function makeRecord(over: Partial<AttachmentRecord>): AttachmentRecord {
+  return {
+    attachmentId: 'att_x',
+    sessionId: SID,
+    filePath: `${WORKDIR}/file`,
+    fileName: 'file',
+    extension: 'pdf',
+    attachmentType: 'document',
+    size: 100,
+    mtimeMs: 1,
+    timestamp: 1,
+    source: 'detected',
+    ...over,
+  };
+}
+
+describe('file-routes preview/thumbnail (COD-38)', () => {
+  let harness: RouteTestHarness;
+
+  beforeEach(async () => {
+    harness = await createRouteTestHarness(registerFileRoutes, { sessionId: SID });
+    vi.clearAllMocks();
+    attachmentRegistry.clearSession(SID);
+  });
+
+  afterEach(async () => {
+    await harness.app.close();
+    attachmentRegistry.clearSession(SID);
+  });
+
+  // ---- workspace-path routes ----
+
+  it('file-preview converts a workspace DOCX to an inline PDF', async () => {
+    const res = await harness.app.inject({ method: 'GET', url: `/api/sessions/${SID}/file-preview?path=deck.docx` });
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['content-type']).toContain('application/pdf');
+    expect(res.headers['content-disposition']).toContain('inline');
+    expect(getOfficePreviewPdfPath).toHaveBeenCalled();
+  });
+
+  it('file-preview redirects a non-Office workspace file (PDF) to the raw route', async () => {
+    const res = await harness.app.inject({ method: 'GET', url: `/api/sessions/${SID}/file-preview?path=report.pdf` });
+    expect(res.statusCode).toBeGreaterThanOrEqual(300);
+    expect(res.statusCode).toBeLessThan(400);
+    expect(res.headers.location).toContain('/file-raw?path=report.pdf');
+    expect(getOfficePreviewPdfPath).not.toHaveBeenCalled();
+  });
+
+  it('file-preview 400s for a missing path parameter', async () => {
+    const res = await harness.app.inject({ method: 'GET', url: `/api/sessions/${SID}/file-preview` });
+    expect(res.statusCode).toBe(400);
+  });
+
+  it('file-thumbnail returns a PNG for a supported workspace file', async () => {
+    const res = await harness.app.inject({ method: 'GET', url: `/api/sessions/${SID}/file-thumbnail?path=deck.pdf` });
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['content-type']).toContain('image/png');
+    expect(res.headers['x-content-type-options']).toBe('nosniff');
+    expect(generateFirstPageThumbnail).toHaveBeenCalled();
+  });
+
+  it('file-thumbnail 400s for an unsupported extension', async () => {
+    const res = await harness.app.inject({ method: 'GET', url: `/api/sessions/${SID}/file-thumbnail?path=notes.exe` });
+    expect(res.statusCode).toBe(400);
+    expect(generateFirstPageThumbnail).not.toHaveBeenCalled();
+  });
+
+  // ---- by-attachmentId routes ----
+
+  it('by-id preview converts a registered DOCX attachment', async () => {
+    attachmentRegistry.register(
+      makeRecord({
+        attachmentId: 'att_docx',
+        filePath: `${WORKDIR}/deck.docx`,
+        fileName: 'deck.docx',
+        extension: 'docx',
+      })
+    );
+    const res = await harness.app.inject({
+      method: 'GET',
+      url: `/api/sessions/${SID}/attachments/att_docx/preview`,
+    });
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['content-type']).toContain('application/pdf');
+  });
+
+  it('by-id preview redirects a non-Office attachment (PNG) to its raw route', async () => {
+    attachmentRegistry.register(
+      makeRecord({ attachmentId: 'att_png', filePath: `${WORKDIR}/shot.png`, fileName: 'shot.png', extension: 'png' })
+    );
+    const res = await harness.app.inject({
+      method: 'GET',
+      url: `/api/sessions/${SID}/attachments/att_png/preview`,
+    });
+    expect(res.statusCode).toBeGreaterThanOrEqual(300);
+    expect(res.statusCode).toBeLessThan(400);
+    expect(res.headers.location).toContain('/attachments/att_png/raw');
+  });
+
+  it('by-id thumbnail returns a PNG for a registered attachment', async () => {
+    attachmentRegistry.register(
+      makeRecord({ attachmentId: 'att_pdf', filePath: `${WORKDIR}/deck.pdf`, fileName: 'deck.pdf', extension: 'pdf' })
+    );
+    const res = await harness.app.inject({
+      method: 'GET',
+      url: `/api/sessions/${SID}/attachments/att_pdf/thumbnail`,
+    });
+    expect(res.statusCode).toBe(200);
+    expect(res.headers['content-type']).toContain('image/png');
+  });
+});