fix(enrichment): blame-link deleted-file + old-line clarity fixes (#2034)

Address review nits:
- Handle removed files without requiring a patch: status === "removed" now
  blames via the file path alone (anchored to line 1), so a deleted file with a
  binary/truncated diff is no longer silently skipped despite the analyzer
  claiming to cover deletes.
- Render the coordinate explicitly as `(old line N)` instead of `file:line`,
  which read like a current line — the value is the OLD-file line.
- Give the commit→PR association call its own diagnostics subcall
  ("github-commit-pulls") instead of sharing "github-commits", for precise
  per-subcall diagnostics (shared endpoint budget unchanged).
- Tests: a shifted-hunk case pinning the old-line semantics (+ its render) and a
  patchless removed-file case.

review-enrichment: 402/402 pass.

Author: nickmopen

review-enrichment/src/analyzers/blame-link.ts

@@ -75,6 +75,7 @@ async function fetchGithubJson<T>(
   fetchFn: typeof fetch,
   signal: AbortSignal | undefined,
   options: Pick<ScanOptions, "analysis" | "diagnostics">,
+  subcall: string,
 ): Promise<T | null> {
   const fetchOptions = {
     endpointCategory: "github-commits",
@@ -83,7 +84,7 @@ async function fetchGithubJson<T>(
     fetchImpl: fetchFn,
     diagnostics: options.diagnostics,
     phase: "blame-link",
-    subcall: "github-commits",
+    subcall,
     maxBytes: 256 * 1024,
     maxCallsPerCategory: MAX_LOOKUPS,
   };
@@ -109,7 +110,7 @@ export async function fetchLatestCommitSha(
   const url =
     `${GITHUB_API}/repos/${encodeURIComponent(owner)}/${encodeURIComponent(repo)}/commits` +
     `?path=${encodeURIComponent(path)}&per_page=1${shaQuery}`;
-  const commits = await fetchGithubJson<CommitListItem[]>(url, headers, fetchFn, signal, options);
+  const commits = await fetchGithubJson<CommitListItem[]>(url, headers, fetchFn, signal, options, "github-commits");
   const sha = Array.isArray(commits) ? commits[0]?.sha : undefined;
   return typeof sha === "string" && sha ? sha : null;
 }
@@ -125,7 +126,7 @@ export async function fetchPrForCommit(
   options: Pick<ScanOptions, "analysis" | "diagnostics">,
 ): Promise<number | null> {
   const url = `${GITHUB_API}/repos/${encodeURIComponent(owner)}/${encodeURIComponent(repo)}/commits/${encodeURIComponent(sha)}/pulls`;
-  const pulls = await fetchGithubJson<AssociatedPr[]>(url, headers, fetchFn, signal, options);
+  const pulls = await fetchGithubJson<AssociatedPr[]>(url, headers, fetchFn, signal, options, "github-commit-pulls");
   const number = Array.isArray(pulls) ? pulls[0]?.number : undefined;
   return typeof number === "number" ? number : null;
 }
@@ -150,9 +151,12 @@ export async function scanBlameLink(
   // additions (a patch with no deletion line has no prior author to attribute).
   const candidates: Array<{ path: string; line: number }> = [];
   for (const file of files) {
-    if (file.status === "added" || SKIP_RE.test(file.path) || !file.patch) continue;
-    const line = firstTouchedOldLine(file.patch);
-    if (line === null) continue;
+    if (file.status === "added" || SKIP_RE.test(file.path)) continue;
+    let line = file.patch ? firstTouchedOldLine(file.patch) : null;
+    // A removed file is entirely a deletion: its path alone drives the history lookup even when the diff carries no
+    // usable patch (binary/truncated). Anchor to line 1 as the representative point.
+    if (line === null && file.status === "removed") line = 1;
+    if (line === null) continue; // a modified file with only additions / no usable patch → nothing to blame
     candidates.push({ path: file.path, line });
     if (candidates.length >= MAX_FILES_PROBED) break;
   }

review-enrichment/src/analyzers/registry.ts

@@ -470,7 +470,7 @@ export const ANALYZER_DESCRIPTORS = [
               ? `commit ${helpers.safeCodeSpan(item.introducedByShaPrefix)}`
               : "an unknown prior change";
         lines.push(
-          `- ${helpers.safeCodeSpan(`${item.file}:${item.line}`)} was most recently introduced by ${origin}`,
+          `- ${helpers.safeCodeSpan(item.file)} (old line ${item.line}) was most recently introduced by ${origin}`,
         );
       }
       return lines;

review-enrichment/test/blame-link.test.ts

@@ -51,6 +51,26 @@ test("scanBlameLink: resolves the originating PR for a modified line", async ()
   assert.match(brief, /#42/);
 });
 
+test("scanBlameLink: reports the OLD-file line on a shifted hunk, and renders it as an old line", async () => {
+  const findings = await scanBlameLink(
+    // hunk shifted: old side starts at 20, new side at 25 — the blamed coordinate is the OLD line, not the new one
+    req([{ path: "src/app.ts", status: "modified", patch: "@@ -20,3 +25,3 @@\n keep\n-old\n+new\n" }], { baseSha: "b" }),
+    routedFetch({ commitSha: "abcdef1234567890", prNumber: 5 }),
+  );
+  assert.equal(findings[0].line, 21); // old 20 (header) + 1 context; NOT the new-side 26
+  assert.match(renderBrief({ blameLink: findings }).promptSection, /old line 21/);
+});
+
+test("scanBlameLink: a removed file is blamed via its path even without a patch", async () => {
+  const findings = await scanBlameLink(
+    req([{ path: "src/gone.ts", status: "removed" }], { baseSha: "b" }),
+    routedFetch({ commitSha: "abcdef1234567890", prNumber: 8 }),
+  );
+  assert.deepEqual(findings, [
+    { file: "src/gone.ts", line: 1, introducedByShaPrefix: "abcdef123456", introducedByPr: 8 },
+  ]);
+});
+
 test("scanBlameLink: a commit with no associated PR still surfaces the SHA prefix", async () => {
   const findings = await scanBlameLink(
     req([{ path: "src/app.ts", status: "modified", patch: modifyPatch(1) }]),