Record why a document's index attempt failed and say so

A content-index attempt that failed (raster failure, a scan with no
text layer, a provider error) recorded its reason only in the server's
observability stream. In the vault, hasContentIndex false looked
identical for a document nobody ever tried and one that failed three
times, and the detail sheet had nothing to say about either.

Apply the summaryState pattern to the index. Two additive columns on
InboundDocument (migration 0333) record when the last attempt finished
and why it produced no index, as a closed reason set: local-empty,
local-unsupported, decrypt-error, raster-failed, provider-error,
pdf-needs-anthropic, empty-transcription. The writer sits at the choke
point the auto job and the corpus backfill share, and in the manual
index route; a success clears the reason. The provider path's specific
failure now survives the local fallback, since "no text" is less
actionable than "the PDF would not render". rasterizePdf names its
failure class so a build that cannot rasterize at all is distinguished
from a PDF that would not render. New guard in both index paths: an
empty provider transcription never becomes a successful empty index.

The detail sheet renders the reason in plain words (muted, six
locales). The DTO and OpenAPI carry the two fields; the disaster
recovery backup and restore carry them verbatim like their summary
siblings.

Refs #776

src/components/documents/__tests__/document-ai-section.test.tsx

@@ -213,3 +213,44 @@ describe("<DocumentAiSection>", () => {
     expect(html).toContain("Summarise");
   });
 });
+
+describe("<DocumentAiSection> index outcome (#776)", () => {
+  it("explains a failed index attempt in plain words, muted", () => {
+    const html = render(
+      base({ hasContentIndex: false, lastIndexOutcome: "local-empty" }),
+    );
+    expect(html).toContain('data-slot="document-index-outcome"');
+    expect(html).toContain("No readable text was found");
+    expect(html).toContain("text-muted-foreground");
+  });
+
+  it("also explains it on the auto-read unread branch", () => {
+    const html = render(
+      base({
+        autoReadEnabled: true,
+        hasContentIndex: false,
+        lastIndexOutcome: "raster-failed",
+      }),
+    );
+    expect(html).toContain('data-slot="document-index-outcome"');
+    expect(html).toContain("couldn&#x27;t be rendered");
+  });
+
+  it("says nothing once the document IS indexed (a past failure is history)", () => {
+    const html = render(
+      base({
+        hasContentIndex: true,
+        contentIndexSource: "vision",
+        lastIndexOutcome: "provider-error",
+      }),
+    );
+    expect(html).not.toContain('data-slot="document-index-outcome"');
+  });
+
+  it("says nothing when no attempt ever ran (never tried is not a failure)", () => {
+    const html = render(
+      base({ hasContentIndex: false, lastIndexOutcome: null }),
+    );
+    expect(html).not.toContain('data-slot="document-index-outcome"');
+  });
+});

src/components/documents/__tests__/document-card.test.tsx

@@ -34,6 +34,8 @@ function doc(overrides: Partial<InboundDocumentDto> = {}): InboundDocumentDto {
     servingClass: "inline",
     hasContentIndex: false,
     contentIndexSource: null,
+    lastIndexAttemptAt: null,
+    lastIndexOutcome: null,
     hasThumbnail: false,
     createdAt: "2025-10-05T08:00:00.000Z",
     updatedAt: "2025-10-05T08:00:00.000Z",

src/components/documents/__tests__/document-facts-review.test.tsx

@@ -85,6 +85,8 @@ function doc(
     servingClass: "inline",
     hasContentIndex: true,
     contentIndexSource: "vision",
+    lastIndexAttemptAt: null,
+    lastIndexOutcome: null,
     hasThumbnail: false,
     createdAt: "2026-08-01T10:00:00.000Z",
     updatedAt: "2026-08-01T10:00:00.000Z",

src/components/documents/__tests__/episode-documents-card.test.tsx

@@ -54,6 +54,8 @@ function doc(id: string, title: string): InboundDocumentDto {
     servingClass: "inline",
     hasContentIndex: false,
     contentIndexSource: null,
+    lastIndexAttemptAt: null,
+    lastIndexOutcome: null,
     hasThumbnail: false,
     createdAt: "2025-10-05T08:00:00.000Z",
     updatedAt: "2025-10-05T08:00:00.000Z",

src/components/documents/__tests__/vault-utils.test.ts

@@ -42,6 +42,8 @@ function doc(overrides: Partial<InboundDocumentDto> = {}): InboundDocumentDto {
     servingClass: "inline",
     hasContentIndex: false,
     contentIndexSource: null,
+    lastIndexAttemptAt: null,
+    lastIndexOutcome: null,
     hasThumbnail: false,
     createdAt: "2026-03-11T08:00:00.000Z",
     updatedAt: "2026-03-11T08:00:00.000Z",

src/components/documents/document-ai-section.tsx

@@ -38,6 +38,7 @@ import { cn } from "@/lib/utils";
 import {
   isAiReadSource,
   type DocumentContentIndexSourceValue,
+  type DocumentIndexOutcomeValue,
   type DocumentSuggestionDto,
   type DocumentSummaryMode,
 } from "@/lib/validations/inbound-documents";
@@ -74,6 +75,7 @@ export function DocumentAiSection({
   onCloseSummary,
   hasContentIndex,
   contentIndexSource,
+  lastIndexOutcome = null,
   indexPending,
   onIndex,
 }: {
@@ -111,11 +113,24 @@ export function DocumentAiSection({
   onCloseSummary: () => void;
   hasContentIndex: boolean;
   contentIndexSource: DocumentContentIndexSourceValue | null;
+  /**
+   * Refs #776 — why the last index attempt produced no index (null: never
+   * tried, or the document IS indexed). Rendered as a muted plain-words line
+   * beside the read action so a failed read is explainable, not a mystery.
+   */
+  lastIndexOutcome?: DocumentIndexOutcomeValue | null;
   indexPending: boolean;
   onIndex: () => void;
 }) {
   const { t } = useTranslations();
   const aiRead = hasContentIndex && isAiReadSource(contentIndexSource);
+  // Refs #776 — only an un-indexed document explains itself; once an index
+  // exists the last failure is history. Muted per the text-colour rule: this
+  // is meta about the document, not content.
+  const indexOutcomeText =
+    !hasContentIndex && lastIndexOutcome
+      ? t(`documents.detail.index.outcome.${lastIndexOutcome}`)
+      : null;
   const readLabel = indexPending
     ? t("documents.ai.reading")
     : aiRead
@@ -233,6 +248,15 @@ export function DocumentAiSection({
             </div>
           ) : null}
 
+          {indexOutcomeText ? (
+            <p
+              data-slot="document-index-outcome"
+              className="text-muted-foreground text-xs"
+            >
+              {indexOutcomeText}
+            </p>
+          ) : null}
+
           {suggestErrorKey ? (
             <p role="alert" className="text-destructive text-sm">
               {suggestErrorKey}

src/components/documents/document-detail-sheet.tsx

@@ -875,6 +875,7 @@ export function DocumentDetailSheet({
                 }}
                 hasContentIndex={doc.hasContentIndex}
                 contentIndexSource={doc.contentIndexSource}
+                lastIndexOutcome={doc.lastIndexOutcome}
                 indexPending={indexDoc.isPending}
                 onIndex={runIndex}
               />