feat(ingest): route DOCX/XLSX/PPTX/images through docmark (ADR-0013)

Wires the sovereign docmark MCP server (git.d-ma.be/mathias/docmark) as the
converter for formats ingestion previously couldn't handle at all -- DOCX,
XLSX, PPTX, PNG/JPG. A single self-contained tools/call POST (docmark runs
stateless_http, no session handshake needed) does the conversion.

- internal/extract/docmark.go: extractViaDocmark(path) -- reads DOCMARK_URL +
  DOCMARK_BEARER_TOKEN from env, base64-encodes the file, calls docmark's
  convert_to_markdown tool, surfaces tool/HTTP errors with context.
- internal/extract/extract.go: routes .docx/.xlsx/.pptx/.png/.jpg/.jpeg to it.
- internal/api/handler.go: isSupportedExtension() replaces the static
  supportedExtensions map -- the new extensions are gated on DOCMARK_URL being
  set, checked per-request. When DOCMARK_URL is unset (e.g. this repo's
  current deployed state), behavior is byte-for-byte unchanged from today:
  same 400/silent-skip as before. Zero risk until the env var is actually
  wired in infra.

TDD throughout: docmark.go tested via httptest mock (success, not-configured,
tool-error, HTTP-error, all 6 new extensions route correctly); handler-level
test proves the DOCMARK_URL gate (docx 400 when unset, 200 when a working
mock is configured). Full task check green (fmt/vet/govulncheck/all tests).

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

ingestion/internal/api/handler.go

@@ -345,11 +345,19 @@ func (h *Handler) Ingest(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, ingestResponse{Pages: pages, Warnings: warnings})
 }
 
-// supportedExtensions lists file extensions that IngestPath will process.
-var supportedExtensions = map[string]bool{
-	".md":  true,
-	".txt": true,
-	".pdf": true,
+// isSupportedExtension reports whether IngestPath will process ext.
+// .docx/.xlsx/.pptx/.png/.jpg/.jpeg require docmark (ADR-0013) and are only
+// supported when DOCMARK_URL is configured — checked per-call (not cached at
+// package init) so it reflects the environment at request time.
+func isSupportedExtension(ext string) bool {
+	switch ext {
+	case ".md", ".txt", ".pdf":
+		return true
+	case ".docx", ".xlsx", ".pptx", ".png", ".jpg", ".jpeg":
+		return os.Getenv("DOCMARK_URL") != ""
+	default:
+		return false
+	}
 }
 
 // IngestPath handles POST /ingest-path — ingest a file or directory.
@@ -382,7 +390,7 @@ func (h *Handler) IngestPath(w http.ResponseWriter, r *http.Request) {
 				return nil
 			}
 			ext := strings.ToLower(filepath.Ext(path))
-			if !supportedExtensions[ext] {
+			if !isSupportedExtension(ext) {
 				return nil
 			}
 			content, readErr := extract.Text(path)
@@ -410,7 +418,7 @@ func (h *Handler) IngestPath(w http.ResponseWriter, r *http.Request) {
 		}
 	} else {
 		ext := strings.ToLower(filepath.Ext(req.Path))
-		if !supportedExtensions[ext] {
+		if !isSupportedExtension(ext) {
 			writeError(w, http.StatusBadRequest, fmt.Sprintf("unsupported file extension: %s", ext))
 			return
 		}

ingestion/internal/api/ingestpath_docmark_test.go

@@ -0,0 +1,61 @@
+// ingestion/internal/api/ingestpath_docmark_test.go
+package api_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIngestPath_DocxUnsupportedWhenDocmarkNotConfigured(t *testing.T) {
+	t.Setenv("DOCMARK_URL", "")
+	_, h := setup(t)
+
+	dir := t.TempDir()
+	f := filepath.Join(dir, "doc.docx")
+	require.NoError(t, os.WriteFile(f, []byte("fake docx"), 0o644))
+
+	body, _ := json.Marshal(map[string]any{"path": f, "source": "test-doc", "dry_run": true})
+	req := httptest.NewRequest(http.MethodPost, "/ingest-path", bytes.NewReader(body))
+	rec := httptest.NewRecorder()
+
+	h.IngestPath(rec, req)
+
+	assert.Equal(t, http.StatusBadRequest, rec.Code, rec.Body.String())
+}
+
+func TestIngestPath_DocxSupportedWhenDocmarkConfigured(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"jsonrpc":"2.0","id":1,"result":{"content":[{"type":"text","text":"# Converted Doc"}]}}`))
+	}))
+	defer srv.Close()
+	t.Setenv("DOCMARK_URL", srv.URL+"/mcp")
+	t.Setenv("DOCMARK_BEARER_TOKEN", "tok")
+
+	_, h := setup(t)
+
+	dir := t.TempDir()
+	f := filepath.Join(dir, "doc.docx")
+	require.NoError(t, os.WriteFile(f, []byte("fake docx"), 0o644))
+
+	body, _ := json.Marshal(map[string]any{"path": f, "source": "test-doc", "dry_run": true})
+	req := httptest.NewRequest(http.MethodPost, "/ingest-path", bytes.NewReader(body))
+	rec := httptest.NewRecorder()
+
+	h.IngestPath(rec, req)
+
+	require.Equal(t, http.StatusOK, rec.Code, rec.Body.String())
+	var resp map[string]any
+	require.NoError(t, json.Unmarshal(rec.Body.Bytes(), &resp))
+	pages, ok := resp["pages"].([]any)
+	require.True(t, ok)
+	assert.NotEmpty(t, pages)
+}