fix(bootstrap): guard bootstrap name checks against undefined names (#85523) (#85615)

* fix(bootstrap): guard bootstrap name checks against undefined names

Add optional chaining to isAgentsBootstrapFile and isAgentsBootstrapName
to prevent TypeError: Cannot read properties of undefined (reading 'toLowerCase')
when bootstrap file entries have undefined name properties.

This crash was observed in 2026.5.20 where a workspace bootstrap file entry
with an undefined name caused every incoming message to fail during bootstrap
context building, completely blocking all agent replies.

Fixes #85523

* test(agents): cover unnamed bootstrap truncation entries

* test(agents): keep bootstrap truncation fixture typed

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/agents/bootstrap-budget.test.ts

@@ -103,6 +103,29 @@ describe("analyzeBootstrapBudget", () => {
 });
 
 describe("bootstrap prompt warnings", () => {
+  it("handles malformed truncation entries without names", () => {
+    const analysis = analyzeBootstrapBudget({
+      files: [
+        {
+          name: "TEMP.md",
+          path: "/tmp/unknown",
+          missing: false,
+          rawChars: 10,
+          injectedChars: 1,
+          truncated: true,
+        },
+      ],
+      bootstrapMaxChars: 5,
+      bootstrapTotalMaxChars: 5,
+    });
+    (analysis.truncatedFiles[0] as { name?: string }).name = undefined;
+
+    const lines = formatBootstrapTruncationWarningLines({
+      analysis,
+    });
+    expect(lines.join("\n")).toContain("10 raw -> 1 injected");
+  });
+
   it("appends warning details to the turn prompt instead of mutating the system prompt", () => {
     const prompt = appendBootstrapPromptWarning("Please continue.", [
       "AGENTS.md: 200 raw -> 0 injected",

src/agents/bootstrap-budget.ts

@@ -68,8 +68,8 @@ function formatWarningCause(cause: BootstrapTruncationCause): string {
   return cause === "per-file-limit" ? "max/file" : "max/total";
 }
 
-function isAgentsBootstrapName(name: string): boolean {
-  return name.toLowerCase() === "agents.md";
+function isAgentsBootstrapName(name: string | undefined): boolean {
+  return name?.toLowerCase() === "agents.md";
 }
 
 function normalizeSeenSignatures(signatures?: string[]): string[] {

src/agents/pi-embedded-helpers.buildbootstrapcontextfiles.test.ts

@@ -241,6 +241,21 @@ describe("buildBootstrapContextFiles", () => {
       warnings.filter((warning) => !warning.includes('missing or invalid "path" field')),
     ).toStrictEqual([]);
   });
+
+  it("handles undefined file names without crashing", () => {
+    const fileWithUndefinedName = {
+      name: undefined,
+      path: "/tmp/test.md",
+      content: "content",
+      missing: false,
+    } as unknown as WorkspaceBootstrapFile;
+    const warnings: string[] = [];
+    const result = buildBootstrapContextFiles([fileWithUndefinedName], {
+      warn: (msg) => warnings.push(msg),
+    });
+    expect(result).toBeDefined();
+    expect(Array.isArray(result)).toBe(true);
+  });
 });
 
 type BootstrapLimitResolverCase = {

src/agents/pi-embedded-helpers/bootstrap.ts

@@ -151,8 +151,8 @@ export function resolveBootstrapPromptTruncationWarningMode(
   return DEFAULT_BOOTSTRAP_PROMPT_TRUNCATION_WARNING_MODE;
 }
 
-function isAgentsBootstrapFile(fileName: string): boolean {
-  return fileName.toLowerCase() === AGENTS_BOOTSTRAP_FILENAME.toLowerCase();
+function isAgentsBootstrapFile(fileName: string | undefined): boolean {
+  return fileName?.toLowerCase() === AGENTS_BOOTSTRAP_FILENAME.toLowerCase();
 }
 
 function isPolicyDigestCandidate(line: string): boolean {