fix(agents): persist spill metadata for elision recovery

Preserve fullOutputPath plus partial-spill metadata when oversized tool-result details are summarized for persistence. This keeps aggregate elision from relabeling capped or source-truncated web_fetch spill files as complete after reload.

src/agents/session-tool-result-guard.tool-result-persist-hook.test.ts

@@ -437,6 +437,8 @@ describe("tool_result_persist hook", () => {
         cwd: "/tmp/".concat("workspace/".repeat(400)),
         name: "oversized fallback command ".repeat(200),
         fullOutputPath: "/tmp/".concat("output/".repeat(400)),
+        spilledChars: 2_000_000,
+        spillTruncated: true,
         aggregated: "x".repeat(120_000),
         tail: "tail ".repeat(800),
         sessions: Array.from({ length: 10 }, (_, i) => ({
@@ -453,6 +455,8 @@ describe("tool_result_persist hook", () => {
     expect(details.persistedDetailsTruncated).toBe(true);
     expect(details.finalDetailsTruncated).toBe(true);
     expect(details.status?.token).toBe("***");
+    expect(details.spilledChars).toBe(2_000_000);
+    expect(details.spillTruncated).toBe(true);
     expect(serialized).not.toContain(tokenValue);
   });
 

src/agents/session-tool-result-guard.ts

@@ -344,7 +344,17 @@ function buildPersistedDetailsFallback(
   }
   if (src) {
     fallback.originalDetailKeys = redactedOriginalDetailKeys(src, redactionConfig);
-    for (const key of ["status", "sessionId", "pid", "exitCode", "exitSignal", "truncated"]) {
+    for (const key of [
+      "status",
+      "sessionId",
+      "pid",
+      "exitCode",
+      "exitSignal",
+      "truncated",
+      "fullOutputPath",
+      "spilledChars",
+      "spillTruncated",
+    ]) {
       const field = src[key];
       if (field !== undefined) {
         fallback[key] = redactPersistedSummaryField(
@@ -470,6 +480,8 @@ function sanitizeToolResultDetailsForPersistence(
     "totalChars",
     "truncated",
     "fullOutputPath",
+    "spilledChars",
+    "spillTruncated",
     "truncation",
   ]) {
     const field = src[key];