log AnonymousError context detail in serialized output

Surface the path/repo/url tied to an AnonymousError when it gets
serialized for logging — previously logs only carried name, message,
and httpStatus, which made file_not_found entries impossible to trace
back to a specific file or repo. Extract the existing detail formatting
out of toString() into a public detail() method, harden it against
AnonymizedFile getters that can throw, and have serializeError include
the result as a "detail" field.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/core/AnonymousError.ts

@@ -27,21 +27,37 @@ export default class AnonymousError extends CustomError {
     this.cause = opt?.cause;
   }
 
-  toString(): string {
-    let out = "";
-    let detail = this.value ? JSON.stringify(this.value) : null;
-    if (this.value instanceof Repository) {
-      detail = this.value.repoId;
-    } else if (this.value instanceof AnonymizedFile) {
-      detail = `/r/${this.value.repository.repoId}/${this.value.anonymizedPath}`;
-    } else if (this.value instanceof GitHubRepository) {
-      detail = `${this.value.fullName}`;
-    } else if (this.value instanceof User) {
-      detail = `${this.value.username}`;
-    } else if (this.value instanceof GitHubBase) {
-      detail = `GHDownload ${this.value.data.repoId}`;
+  detail(): string | undefined {
+    if (this.value == null) return undefined;
+    try {
+      if (this.value instanceof Repository) return this.value.repoId;
+      if (this.value instanceof AnonymizedFile) {
+        const repoId = this.value.repository?.repoId;
+        // anonymizedPath getter can throw if the file isn't initialized;
+        // fall back to whatever path is known.
+        let p: string | undefined;
+        try {
+          p = this.value.anonymizedPath;
+        } catch {
+          p = this.value.filePath;
+        }
+        return repoId ? `/r/${repoId}/${p ?? ""}` : p;
+      }
+      if (this.value instanceof GitHubRepository) return this.value.fullName;
+      if (this.value instanceof User) return this.value.username;
+      if (this.value instanceof GitHubBase) {
+        return `GHDownload ${this.value.data.repoId}`;
+      }
+      if (typeof this.value === "string") return this.value;
+      return JSON.stringify(this.value);
+    } catch {
+      return String(this.value);
     }
-    out += this.message;
+  }
+
+  toString(): string {
+    let out = this.message;
+    const detail = this.detail();
     if (detail) {
       out += `: ${detail}`;
     }

src/core/logger.ts

@@ -140,6 +140,7 @@ type ErrorLike = {
   cause?: unknown;
   request?: { url?: string; method?: string };
   response?: { url?: string; status?: number };
+  detail?: () => string | undefined;
 };
 
 export function serializeError(err: unknown): Record<string, unknown> {
@@ -161,6 +162,14 @@ export function serializeError(err: unknown): Record<string, unknown> {
   // AnonymousError carries an httpStatus and an inner cause.
   if (typeof e.httpStatus === "number") out.httpStatus = e.httpStatus;
   if (e.code !== undefined && e.code !== e.message) out.code = e.code;
+  if (typeof e.detail === "function") {
+    try {
+      const d = e.detail();
+      if (d) out.detail = d;
+    } catch {
+      /* ignore */
+    }
+  }
   if (e.cause) out.cause = serializeError(e.cause);
 
   // Only include the stack when there's nothing else useful — avoids dumping