diff --git a/test/helpers/pty-transcript-cost.unit.test.ts b/test/helpers/pty-transcript-cost.unit.test.ts
index c02e5db07..d05d3591e 100644
--- a/test/helpers/pty-transcript-cost.unit.test.ts
+++ b/test/helpers/pty-transcript-cost.unit.test.ts
@@ -45,6 +45,7 @@ describe('ptyTranscriptCostUsd', () => {
     const unpriced = fixture(project => fs.writeFileSync(path.join(project, `${SID}.jsonl`),
       assistant('msg_a', 'claude-opus-5-5', { output_tokens: 1 }) + '\n' + assistant('msg_b', 'some-unpriced-model', { output_tokens: 1 }) + '\n'));
     const empty = fixture(project => fs.writeFileSync(path.join(project, `${SID}.jsonl`), JSON.stringify({ type: 'user', sessionId: SID }) + '\n'));
+    const unreadable = fixture(project => fs.mkdirSync(path.join(project, `${SID}.jsonl`)));
     try {
       expect(ptyTranscriptCostUsd(unpriced, SID)).toBeUndefined();
       expect(ptyTranscriptCostUsd(empty, SID)).toBeUndefined();
@@ -53,6 +54,7 @@ describe('ptyTranscriptCostUsd', () => {
       expect(ptyTranscriptCostUsd(null, SID)).toBeUndefined();
       expect(ptyTranscriptCostUsd(path.join(empty, 'missing'), SID)).toBeUndefined();
       expect(pricedTranscript(undefined)).toEqual({});
-    } finally { for (const dir of [unpriced, empty]) fs.rmSync(dir, { recursive: true, force: true }); }
+      expect(ptyTranscriptCostUsd(unreadable, SID)).toBeUndefined();
+    } finally { for (const dir of [unpriced, empty, unreadable]) fs.rmSync(dir, { recursive: true, force: true }); }
   });
 });
diff --git a/test/helpers/pty/transcript-cost.ts b/test/helpers/pty/transcript-cost.ts
index 064d520b8..c54a70bed 100644
--- a/test/helpers/pty/transcript-cost.ts
+++ b/test/helpers/pty/transcript-cost.ts
@@ -12,31 +12,30 @@ export function pricedTranscript(session: { hermeticConfigDir?: string | null; s
  * Price one PTY session from the transcripts Claude Code wrote under its owned config dir:
  * `projects/<dir>/<sessionId>.jsonl` (inline sidechains included) and `projects/<dir>/<sessionId>/subagents/*.jsonl`,
  * rows deduplicated by message id. Undefined (cost-unknown, never $0) without a config dir, session id, transcript or
- * usage, or when a message's model has no price row.
+ * usage, when a message's model has no price row, or when any read fails: it runs in ledger writers before close and
+ * cleanup, so it never throws.
  */
 export function ptyTranscriptCostUsd(configDir: string | null | undefined, sessionId: string | undefined): number | undefined {
   if (!configDir || !sessionId) return undefined;
-  const projects = path.join(configDir, 'projects');
-  let dirs: fs.Dirent[];
   try {
-    dirs = fs.readdirSync(projects, { withFileTypes: true });
+    const projects = path.join(configDir, 'projects');
+    const files: string[] = [];
+    for (const dir of fs.readdirSync(projects, { withFileTypes: true })) {
+      if (!dir.isDirectory()) continue;
+      const main = path.join(projects, dir.name, `${sessionId}.jsonl`);
+      if (fs.existsSync(main)) files.push(main);
+      const subagents = path.join(projects, dir.name, sessionId, 'subagents');
+      if (fs.existsSync(subagents)) files.push(...fs.readdirSync(subagents).filter(f => f.endsWith('.jsonl')).map(f => path.join(subagents, f)));
+    }
+    const rows = files.flatMap(file => fs.readFileSync(file, 'utf8').split('\n').flatMap(line => {
+      try {
+        return [JSON.parse(line)];
+      } catch {
+        return [];
+      }
+    }));
+    return streamedUsageCostUsd(rows);
   } catch {
     return undefined;
   }
-  const files: string[] = [];
-  for (const dir of dirs) {
-    if (!dir.isDirectory()) continue;
-    const main = path.join(projects, dir.name, `${sessionId}.jsonl`);
-    if (fs.existsSync(main)) files.push(main);
-    const subagents = path.join(projects, dir.name, sessionId, 'subagents');
-    if (fs.existsSync(subagents)) files.push(...fs.readdirSync(subagents).filter(f => f.endsWith('.jsonl')).map(f => path.join(subagents, f)));
-  }
-  const rows = files.flatMap(file => fs.readFileSync(file, 'utf8').split('\n').flatMap(line => {
-    try {
-      return [JSON.parse(line)];
-    } catch {
-      return [];
-    }
-  }));
-  return streamedUsageCostUsd(rows);
 }