diff --git a/src/agents/bootstrap-budget.test.ts b/src/agents/bootstrap-budget.test.ts
index d12326b41813..a74c077ec345 100644
--- a/src/agents/bootstrap-budget.test.ts
+++ b/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",
diff --git a/src/agents/bootstrap-budget.ts b/src/agents/bootstrap-budget.ts
index a493d68d9b17..85c43173301e 100644
--- a/src/agents/bootstrap-budget.ts
+++ b/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[] {
diff --git a/src/agents/pi-embedded-helpers.buildbootstrapcontextfiles.test.ts b/src/agents/pi-embedded-helpers.buildbootstrapcontextfiles.test.ts
index f2644ab148be..0042ffbee406 100644
--- a/src/agents/pi-embedded-helpers.buildbootstrapcontextfiles.test.ts
+++ b/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 = {
diff --git a/src/agents/pi-embedded-helpers/bootstrap.ts b/src/agents/pi-embedded-helpers/bootstrap.ts
index bd24fc866e93..80f24537b349 100644
--- a/src/agents/pi-embedded-helpers/bootstrap.ts
+++ b/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 {