fix(agents): trim trailing assistant turns and rewrite blank user messages in session repair

amknight · amknight · commit 07e3179b2079 · 2026-05-01T20:53:08.000+10:00
Session-file repair now: - Trims trailing assistant messages so the JSONL never ends on role=assistant, preventing the Anthropic 400 prefill-loop that fires when thinking is enabled. (#75271) - Rewrites blank-only user messages to a synthetic '(continue)' placeholder instead of dropping them, so strict providers (Qwen/mlx-vlm, Anthropic) no longer reject transcripts missing a user turn. (#75313) Closes #75271, closes #75313.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -34,6 +34,7 @@ Docs: https://docs.openclaw.ai
 - Voice Call CLI: delegate operational `voicecall` commands to the running Gateway runtime and skip webhook startup during CLI-only plugin loading, preventing webhook port conflicts and `setup --json` hangs. Fixes #72345. Thanks @serrurco and @DougButdorf.
 - Agents/pi-embedded-runner: extract the `abortable` provider-call wrapper from `runEmbeddedAttempt` to module scope so its promise handlers no longer close over the run lexical context, releasing transcripts, tool buffers, and subscription callbacks when a provider call hangs past abort. (#74182) Thanks @cjboy007.
 - Docker: restore `python3` in the gateway runtime image after the slim-runtime switch. Fixes #75041.
+- Agents/session-repair: trim trailing assistant messages from session JSONL files so sessions ending on `role=assistant` no longer trigger Anthropic 400 prefill-loop rejections across restarts, and rewrite blank-only user messages to a synthetic `(continue)` placeholder instead of dropping them so strict providers (Qwen/mlx-vlm, Anthropic) no longer reject transcripts missing a user turn. Fixes #75271 and #75313. Thanks @amknight.
 - CLI/Voice Call: scope `voicecall` command activation to the Voice Call plugin so setup and smoke checks no longer broad-load unrelated plugin runtimes or hang after printing JSON. Thanks @vincentkoc.
 - Doctor/plugins: warn when restrictive `plugins.allow` is paired with wildcard or plugin-owned tool allowlists, making the exclusive plugin allowlist behavior visible before users hit empty callable-tool runs. Refs #58009 and #64982. Thanks @KR-Python and @BKF-Gitty.
 - Google Meet/Voice Call: keep Twilio Meet joins in conversation mode and reuse the realtime intro prompt when no voice-call-specific intro is configured, so answered phone bridge calls speak instead of joining silently. Refs #72478. Thanks @DougButdorf.
diff --git a/src/agents/session-file-repair.test.ts b/src/agents/session-file-repair.test.ts
@@ -2,7 +2,7 @@ import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
-import { repairSessionFileIfNeeded } from "./session-file-repair.js";
+import { BLANK_USER_FALLBACK_TEXT, repairSessionFileIfNeeded } from "./session-file-repair.js";
 
 function buildSessionHeaderAndMessage() {
   const header = {
@@ -100,7 +100,7 @@ describe("repairSessionFileIfNeeded", () => {
 
   it("rewrites persisted assistant messages with empty content arrays", async () => {
     const { file } = await createTempSessionPath();
-    const { header } = buildSessionHeaderAndMessage();
+    const { header, message } = buildSessionHeaderAndMessage();
     const poisonedAssistantEntry = {
       type: "message",
       id: "msg-2",
@@ -117,7 +117,16 @@ describe("repairSessionFileIfNeeded", () => {
         errorMessage: "transient stream failure",
       },
     };
-    const original = `${JSON.stringify(header)}\n${JSON.stringify(poisonedAssistantEntry)}\n`;
+    // Include a user follow-up after the poisoned assistant so the session
+    // doesn’t end on assistant (which would also trigger trailing-trim).
+    const followUp = {
+      type: "message",
+      id: "msg-3",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: { role: "user", content: "retry" },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(message)}\n${JSON.stringify(poisonedAssistantEntry)}\n${JSON.stringify(followUp)}\n`;
     await fs.writeFile(file, original, "utf-8");
 
     const warn = vi.fn();
@@ -136,16 +145,17 @@ describe("repairSessionFileIfNeeded", () => {
 
     const repaired = await fs.readFile(file, "utf-8");
     const repairedLines = repaired.trim().split("\n");
-    expect(repairedLines).toHaveLength(2);
+    // header + user + rewritten-assistant + follow-up user
+    expect(repairedLines).toHaveLength(4);
     const repairedEntry: { message: { content: { type: string; text: string }[] } } = JSON.parse(
-      repairedLines[1],
+      repairedLines[2],
     );
     expect(repairedEntry.message.content).toEqual([
       { type: "text", text: "[assistant turn failed before producing content]" },
     ]);
   });
 
-  it("drops persisted blank user text messages", async () => {
+  it("rewrites blank-only user text messages to synthetic placeholder instead of dropping", async () => {
     const { file } = await createTempSessionPath();
     const { header, message } = buildSessionHeaderAndMessage();
     const blankUserEntry = {
@@ -165,13 +175,48 @@ describe("repairSessionFileIfNeeded", () => {
     const result = await repairSessionFileIfNeeded({ sessionFile: file, warn });
 
     expect(result.repaired).toBe(true);
-    expect(result.droppedBlankUserMessages).toBe(1);
-    expect(warn.mock.calls[0]?.[0]).toContain("dropped 1 blank user message(s)");
+    // Blank user messages are now rewritten, not dropped.
+    expect(result.rewrittenUserMessages).toBe(1);
+    expect(result.droppedBlankUserMessages).toBe(0);
+    expect(warn.mock.calls[0]?.[0]).toContain("rewrote 1 user message(s)");
 
     const repaired = await fs.readFile(file, "utf-8");
     const repairedLines = repaired.trim().split("\n");
-    expect(repairedLines).toHaveLength(2);
-    expect(JSON.parse(repairedLines[1])?.id).toBe("msg-1");
+    // Both entries preserved: rewritten blank user + original user.
+    expect(repairedLines).toHaveLength(3);
+    const rewrittenEntry = JSON.parse(repairedLines[1]);
+    expect(rewrittenEntry.id).toBe("msg-blank");
+    expect(rewrittenEntry.message.content).toEqual([
+      { type: "text", text: BLANK_USER_FALLBACK_TEXT },
+    ]);
+  });
+
+  it("rewrites blank string-content user messages to placeholder", async () => {
+    const { file } = await createTempSessionPath();
+    const { header, message } = buildSessionHeaderAndMessage();
+    const blankStringUserEntry = {
+      type: "message",
+      id: "msg-blank-str",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: {
+        role: "user",
+        content: "   ",
+      },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(blankStringUserEntry)}\n${JSON.stringify(message)}\n`;
+    await fs.writeFile(file, original, "utf-8");
+
+    const result = await repairSessionFileIfNeeded({ sessionFile: file });
+
+    expect(result.repaired).toBe(true);
+    expect(result.rewrittenUserMessages).toBe(1);
+
+    const repaired = await fs.readFile(file, "utf-8");
+    const repairedLines = repaired.trim().split("\n");
+    expect(repairedLines).toHaveLength(3);
+    const rewrittenEntry = JSON.parse(repairedLines[1]);
+    expect(rewrittenEntry.message.content).toBe(BLANK_USER_FALLBACK_TEXT);
   });
 
   it("removes blank user text blocks while preserving media blocks", async () => {
@@ -260,7 +305,16 @@ describe("repairSessionFileIfNeeded", () => {
         stopReason: "stop",
       },
     };
-    const original = `${JSON.stringify(header)}\n${JSON.stringify(silentReplyEntry)}\n`;
+    // Append a user follow-up so the session doesn't end on assistant —
+    // this test is about per-entry rewrite behavior, not trailing-trim.
+    const followUp = {
+      type: "message",
+      id: "msg-3",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: { role: "user", content: "follow up" },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(silentReplyEntry)}\n${JSON.stringify(followUp)}\n`;
     await fs.writeFile(file, original, "utf-8");
 
     const result = await repairSessionFileIfNeeded({ sessionFile: file });
@@ -271,6 +325,136 @@ describe("repairSessionFileIfNeeded", () => {
     expect(after).toBe(original);
   });
 
+  it("trims trailing assistant messages from the session file", async () => {
+    const { file } = await createTempSessionPath();
+    const { header, message } = buildSessionHeaderAndMessage();
+    const assistantEntry = {
+      type: "message",
+      id: "msg-asst",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text: "stale answer" }],
+        stopReason: "stop",
+      },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(message)}\n${JSON.stringify(assistantEntry)}\n`;
+    await fs.writeFile(file, original, "utf-8");
+
+    const warn = vi.fn();
+    const result = await repairSessionFileIfNeeded({ sessionFile: file, warn });
+
+    expect(result.repaired).toBe(true);
+    expect(result.trimmedTrailingAssistantMessages).toBe(1);
+    expect(warn.mock.calls[0]?.[0]).toContain("trimmed 1 trailing assistant message(s)");
+
+    const repaired = await fs.readFile(file, "utf-8");
+    const repairedLines = repaired.trim().split("\n");
+    // Only header + user message remain; assistant was trimmed.
+    expect(repairedLines).toHaveLength(2);
+  });
+
+  it("trims multiple consecutive trailing assistant messages", async () => {
+    const { file } = await createTempSessionPath();
+    const { header, message } = buildSessionHeaderAndMessage();
+    const assistantEntry1 = {
+      type: "message",
+      id: "msg-asst-1",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text: "first" }],
+        stopReason: "stop",
+      },
+    };
+    const assistantEntry2 = {
+      type: "message",
+      id: "msg-asst-2",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text: "second" }],
+        stopReason: "stop",
+      },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(message)}\n${JSON.stringify(assistantEntry1)}\n${JSON.stringify(assistantEntry2)}\n`;
+    await fs.writeFile(file, original, "utf-8");
+
+    const result = await repairSessionFileIfNeeded({ sessionFile: file });
+
+    expect(result.repaired).toBe(true);
+    expect(result.trimmedTrailingAssistantMessages).toBe(2);
+
+    const repaired = await fs.readFile(file, "utf-8");
+    const repairedLines = repaired.trim().split("\n");
+    expect(repairedLines).toHaveLength(2);
+  });
+
+  it("does not trim non-trailing assistant messages", async () => {
+    const { file } = await createTempSessionPath();
+    const { header, message } = buildSessionHeaderAndMessage();
+    const assistantEntry = {
+      type: "message",
+      id: "msg-asst",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text: "answer" }],
+        stopReason: "stop",
+      },
+    };
+    const userFollowUp = {
+      type: "message",
+      id: "msg-user-2",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: { role: "user", content: "follow up" },
+    };
+    // Ends on user, so nothing to trim.
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(message)}\n${JSON.stringify(assistantEntry)}\n${JSON.stringify(userFollowUp)}\n`;
+    await fs.writeFile(file, original, "utf-8");
+
+    const result = await repairSessionFileIfNeeded({ sessionFile: file });
+
+    expect(result.repaired).toBe(false);
+    expect(result.trimmedTrailingAssistantMessages ?? 0).toBe(0);
+  });
+
+  it("never trims below the session header", async () => {
+    // Edge case: a session with only a header and trailing assistant messages
+    // should keep the header intact.
+    const { file } = await createTempSessionPath();
+    const { header } = buildSessionHeaderAndMessage();
+    const assistantEntry = {
+      type: "message",
+      id: "msg-asst",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: {
+        role: "assistant",
+        content: [{ type: "text", text: "orphan" }],
+        stopReason: "stop",
+      },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(assistantEntry)}\n`;
+    await fs.writeFile(file, original, "utf-8");
+
+    const result = await repairSessionFileIfNeeded({ sessionFile: file });
+
+    expect(result.repaired).toBe(true);
+    expect(result.trimmedTrailingAssistantMessages).toBe(1);
+
+    const repaired = await fs.readFile(file, "utf-8");
+    const repairedLines = repaired.trim().split("\n");
+    // Only the header remains.
+    expect(repairedLines).toHaveLength(1);
+    expect(JSON.parse(repairedLines[0]).type).toBe("session");
+  });
+
   it("is a no-op on a session that was already repaired", async () => {
     const { file } = await createTempSessionPath();
     const { header } = buildSessionHeaderAndMessage();
@@ -289,7 +473,16 @@ describe("repairSessionFileIfNeeded", () => {
         stopReason: "error",
       },
     };
-    const original = `${JSON.stringify(header)}\n${JSON.stringify(healedEntry)}\n`;
+    // Append a user follow-up so the session doesn't end on assistant —
+    // this test is about idempotent per-entry repair, not trailing-trim.
+    const followUp = {
+      type: "message",
+      id: "msg-3",
+      parentId: null,
+      timestamp: new Date().toISOString(),
+      message: { role: "user", content: "follow up" },
+    };
+    const original = `${JSON.stringify(header)}\n${JSON.stringify(healedEntry)}\n${JSON.stringify(followUp)}\n`;
     await fs.writeFile(file, original, "utf-8");
 
     const result = await repairSessionFileIfNeeded({ sessionFile: file });
diff --git a/src/agents/session-file-repair.ts b/src/agents/session-file-repair.ts
