diff --git a/src/agents/pi-embedded-runner/run/attempt.ts b/src/agents/pi-embedded-runner/run/attempt.ts
index e83c3ae4a..622bdb7f4 100644
--- a/src/agents/pi-embedded-runner/run/attempt.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.ts
@@ -52,6 +52,7 @@ import {
 import { DEFAULT_BOOTSTRAP_FILENAME } from "../../workspace.js";
 import { buildSystemPromptReport } from "../../system-prompt-report.js";
 import { resolveDefaultModelForAgent } from "../../model-selection.js";
+import { sanitizeToolUseResultPairing } from "../../session-transcript-repair.js";
 
 import { isAbortError } from "../abort.js";
 import { buildEmbeddedExtensionPaths } from "../extensions.js";
@@ -535,9 +536,11 @@ export async function runEmbeddedAttempt(
           validated,
           getDmHistoryLimitFromSessionKey(params.sessionKey, params.config),
         );
-        cacheTrace?.recordStage("session:limited", { messages: limited });
-        if (limited.length > 0) {
-          activeSession.agent.replaceMessages(limited);
+        // Fix: Repair tool_use/tool_result pairings AFTER truncation (issue #4367)
+        const repaired = sanitizeToolUseResultPairing(limited);
+        cacheTrace?.recordStage("session:limited", { messages: repaired });
+        if (repaired.length > 0) {
+          activeSession.agent.replaceMessages(repaired);
         }
       } catch (err) {
         sessionManager.flushPendingToolResults?.();
diff --git a/src/agents/subagent-announce.ts b/src/agents/subagent-announce.ts
index 444726efc..46d902e80 100644
--- a/src/agents/subagent-announce.ts
+++ b/src/agents/subagent-announce.ts
@@ -192,6 +192,41 @@ async function maybeQueueSubagentAnnounce(params: {
   return "none";
 }
 
+/**
+ * Build a descriptive error status label from outcome data.
+ * Includes error type, message, and hint if available.
+ */
+function buildErrorStatusLabel(outcome: SubagentRunOutcome): string {
+  const parts: string[] = [];
+
+  // Start with "failed"
+  parts.push("failed");
+
+  // Add error type context
+  if (outcome.errorType) {
+    const typeLabel: Record<string, string> = {
+      model: "API error",
+      tool: "tool error",
+      network: "network error",
+      config: "configuration error",
+      timeout: "timeout",
+    };
+    const label = typeLabel[outcome.errorType] || "error";
+    parts.push(`(${label}):`);
+  }
+
+  // Add error message
+  const errorMsg = outcome.error || "unknown error";
+  parts.push(errorMsg);
+
+  // Add hint if available
+  if (outcome.errorHint) {
+    parts.push(`— ${outcome.errorHint}`);
+  }
+
+  return parts.join(" ");
+}
+
 async function buildSubagentStatsLine(params: {
   sessionKey: string;
   startedAt?: number;
@@ -299,6 +334,8 @@ export function buildSubagentSystemPrompt(params: {
 export type SubagentRunOutcome = {
   status: "ok" | "error" | "timeout" | "unknown";
   error?: string;
+  errorType?: "model" | "tool" | "network" | "config" | "timeout" | "unknown";
+  errorHint?: string;
 };
 
 export async function runSubagentAnnounceFlow(params: {
@@ -380,7 +417,7 @@ export async function runSubagentAnnounceFlow(params: {
         : outcome.status === "timeout"
           ? "timed out"
           : outcome.status === "error"
-            ? `failed: ${outcome.error || "unknown error"}`
+            ? buildErrorStatusLabel(outcome)
             : "finished with unknown status";
 
     // Build instructional message for main agent
diff --git a/src/agents/subagent-registry.ts b/src/agents/subagent-registry.ts
index d325e40e2..dca685b72 100644
--- a/src/agents/subagent-registry.ts
+++ b/src/agents/subagent-registry.ts
@@ -184,7 +184,16 @@ function ensureListener() {
     entry.endedAt = endedAt;
     if (phase === "error") {
       const error = typeof evt.data?.error === "string" ? (evt.data.error as string) : undefined;
-      entry.outcome = { status: "error", error };
+      const errorType =
+        typeof evt.data?.errorType === "string" ? (evt.data.errorType as string) : undefined;
+      const errorHint =
+        typeof evt.data?.errorHint === "string" ? (evt.data.errorHint as string) : undefined;
+      entry.outcome = {
+        status: "error",
+        error,
+        errorType: errorType as SubagentRunOutcome["errorType"],
+        errorHint,
+      };
     } else {
       entry.outcome = { status: "ok" };
     }
diff --git a/src/auto-reply/reply/agent-runner-execution.ts b/src/auto-reply/reply/agent-runner-execution.ts
index 21732f49f..36305bc68 100644
--- a/src/auto-reply/reply/agent-runner-execution.ts
+++ b/src/auto-reply/reply/agent-runner-execution.ts
@@ -51,6 +51,85 @@ export type AgentRunLoopResult =
     }
   | { kind: "final"; payload: ReplyPayload };
 
+/**
+ * Categorize errors to provide better error messages to users.
+ * Returns error message, type, and optional hint for remediation.
+ */
+function categorizeError(err: unknown): {
+  message: string;
+  type: "model" | "tool" | "network" | "config" | "timeout" | "unknown";
+  hint?: string;
+} {
+  const message = err instanceof Error ? err.message : String(err);
+
+  // File system errors
+  if (message.includes("ENOENT") || message.includes("ENOTDIR")) {
+    return { message, type: "tool", hint: "File or directory not found" };
+  }
+  if (message.includes("EACCES") || message.includes("EPERM")) {
+    return { message, type: "tool", hint: "Permission denied" };
+  }
+  if (message.includes("EISDIR")) {
+    return { message, type: "tool", hint: "Expected file but found directory" };
+  }
+
+  // API/Model errors
+  if (message.includes("rate limit") || message.includes("429")) {
+    return { message, type: "model", hint: "Rate limit exceeded - retry in a few moments" };
+  }
+  if (
+    message.includes("401") ||
+    message.includes("unauthorized") ||
+    message.includes("authentication")
+  ) {
+    return { message, type: "config", hint: "Check API credentials and permissions" };
+  }
+  if (message.includes("403") || message.includes("forbidden")) {
+    return { message, type: "config", hint: "Access denied - check permissions" };
+  }
+  if (message.includes("400") || message.includes("invalid request")) {
+    return { message, type: "model", hint: "Invalid request parameters" };
+  }
+  if (message.includes("500") || message.includes("503")) {
+    return { message, type: "model", hint: "API service error - try again later" };
+  }
+  if (message.includes("quota") || message.includes("billing")) {
+    return { message, type: "config", hint: "Check billing and API quota limits" };
+  }
+
+  // Network errors
+  if (message.includes("ECONNREFUSED") || message.includes("ETIMEDOUT")) {
+    return { message, type: "network", hint: "Connection failed - check network connectivity" };
+  }
+  if (message.includes("ENOTFOUND") || message.includes("DNS") || message.includes("EAI_AGAIN")) {
+    return { message, type: "network", hint: "DNS resolution failed - check hostname" };
+  }
+  if (message.includes("ENETUNREACH") || message.includes("EHOSTUNREACH")) {
+    return { message, type: "network", hint: "Network unreachable - check connection" };
+  }
+
+  // Timeout errors
+  if (
+    message.toLowerCase().includes("timeout") ||
+    message.toLowerCase().includes("timed out") ||
+    message.includes("ETIMEDOUT")
+  ) {
+    return { message, type: "timeout", hint: "Operation took too long - try increasing timeout" };
+  }
+
+  // Context/memory errors
+  if (message.includes("context") && message.includes("too large")) {
+    return { message, type: "model", hint: "Conversation too long - try clearing history" };
+  }
+
+  // Missing environment/config
+  if (message.includes("missing") && (message.includes("key") || message.includes("token"))) {
+    return { message, type: "config", hint: "Missing required configuration or credentials" };
+  }
+
+  return { message, type: "unknown" };
+}
+
 export async function runAgentTurnWithFallback(params: {
   commandBody: string;
   followupRun: FollowupRun;
@@ -204,6 +283,7 @@ export async function runAgentTurnWithFallback(params: {
                 return result;
               })
               .catch((err) => {
+                const { message, type, hint } = categorizeError(err);
                 emitAgentEvent({
                   runId,
                   stream: "lifecycle",
@@ -211,7 +291,9 @@ export async function runAgentTurnWithFallback(params: {
                     phase: "error",
                     startedAt,
                     endedAt: Date.now(),
-                    error: err instanceof Error ? err.message : String(err),
+                    error: message,
+                    errorType: type,
+                    errorHint: hint,
                   },
                 });
                 throw err;
diff --git a/src/hooks/llm-slug-generator.test.ts b/src/hooks/llm-slug-generator.test.ts
new file mode 100644
index 000000000..ba65ee6c3
--- /dev/null
+++ b/src/hooks/llm-slug-generator.test.ts
@@ -0,0 +1,313 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { generateSlugViaLLM } from "./llm-slug-generator.js";
+import type { OpenClawConfig } from "../config/config.js";
+import type { EmbeddedPiRunResult } from "../agents/pi-embedded.js";
+
+const runEmbeddedPiAgentMock = vi.fn<
+  Parameters<typeof import("../agents/pi-embedded.js").runEmbeddedPiAgent>,
+  Promise<EmbeddedPiRunResult>
+>();
+
+vi.mock("../agents/pi-embedded.js", () => ({
+  runEmbeddedPiAgent: (...args: unknown[]) => runEmbeddedPiAgentMock(...args),
+}));
+
+describe("generateSlugViaLLM", () => {
+  beforeEach(() => {
+    runEmbeddedPiAgentMock.mockReset();
+  });
+
+  describe("model resolution", () => {
+    it("uses configured default model from agents.defaults.model.primary", async () => {
+      // Arrange: Config with custom default model (Sonnet instead of Opus)
+      const cfg: OpenClawConfig = {
+        agents: {
+          defaults: {
+            model: {
+              primary: "anthropic/claude-sonnet-4-5",
+            },
+          },
+        },
+      };
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "test-slug" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      // Act
+      await generateSlugViaLLM({
+        sessionContent: "Some conversation about testing",
+        cfg,
+      });
+
+      // Assert: Should use Sonnet, not hardcoded Opus
+      expect(runEmbeddedPiAgentMock).toHaveBeenCalledTimes(1);
+      const callArgs = runEmbeddedPiAgentMock.mock.calls[0]?.[0];
+      expect(callArgs).toMatchObject({
+        provider: "anthropic",
+        model: "claude-sonnet-4-5",
+        config: cfg,
+      });
+    });
+
+    it("uses configured default model with custom provider", async () => {
+      // Arrange: Config with OpenRouter model
+      const cfg: OpenClawConfig = {
+        agents: {
+          defaults: {
+            model: {
+              primary: "openrouter/anthropic/claude-3.5-sonnet",
+            },
+          },
+        },
+      };
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "custom-provider-slug" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      // Act
+      await generateSlugViaLLM({
+        sessionContent: "Testing custom provider",
+        cfg,
+      });
+
+      // Assert: Should use OpenRouter provider
+      expect(runEmbeddedPiAgentMock).toHaveBeenCalledTimes(1);
+      const callArgs = runEmbeddedPiAgentMock.mock.calls[0]?.[0];
+      expect(callArgs).toMatchObject({
+        provider: "openrouter",
+        model: "anthropic/claude-3.5-sonnet",
+        config: cfg,
+      });
+    });
+
+    it("falls back to DEFAULT_MODEL when no model.primary is configured", async () => {
+      // Arrange: Empty config (no custom model)
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "default-model-slug" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      // Act
+      await generateSlugViaLLM({
+        sessionContent: "Testing default fallback",
+        cfg,
+      });
+
+      // Assert: Should fall back to DEFAULT_MODEL (claude-opus-4-5)
+      expect(runEmbeddedPiAgentMock).toHaveBeenCalledTimes(1);
+      const callArgs = runEmbeddedPiAgentMock.mock.calls[0]?.[0];
+      expect(callArgs).toMatchObject({
+        provider: "anthropic",
+        model: "claude-opus-4-5",
+        config: cfg,
+      });
+    });
+
+    it("uses Haiku when configured as default model", async () => {
+      // Arrange: Config with Haiku as default
+      const cfg: OpenClawConfig = {
+        agents: {
+          defaults: {
+            model: {
+              primary: "anthropic/claude-3-5-haiku-20241022",
+            },
+          },
+        },
+      };
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "haiku-slug" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      // Act
+      await generateSlugViaLLM({
+        sessionContent: "Budget-friendly slug generation",
+        cfg,
+      });
+
+      // Assert: Should use Haiku
+      expect(runEmbeddedPiAgentMock).toHaveBeenCalledTimes(1);
+      const callArgs = runEmbeddedPiAgentMock.mock.calls[0]?.[0];
+      expect(callArgs).toMatchObject({
+        provider: "anthropic",
+        model: "claude-3-5-haiku-20241022",
+        config: cfg,
+      });
+    });
+  });
+
+  describe("slug generation", () => {
+    it("generates valid slug from LLM response", async () => {
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "api-design" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      const slug = await generateSlugViaLLM({
+        sessionContent: "Discussion about API design patterns",
+        cfg,
+      });
+
+      expect(slug).toBe("api-design");
+    });
+
+    it("cleans up LLM response with extra characters", async () => {
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "  Bug Fix!  " }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      const slug = await generateSlugViaLLM({
+        sessionContent: "Bug fix discussion",
+        cfg,
+      });
+
+      expect(slug).toBe("bug-fix");
+    });
+
+    it("truncates long slugs to 30 characters", async () => {
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "this-is-a-very-long-slug-that-should-be-truncated-significantly" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      const slug = await generateSlugViaLLM({
+        sessionContent: "Long discussion",
+        cfg,
+      });
+
+      // Verify length is enforced (implementation slices before final cleanup)
+      expect(slug?.length).toBeLessThanOrEqual(30);
+      expect(slug).toMatch(/^this-is-a-very-long-slug/);
+    });
+
+    it("returns null when LLM returns no payloads", async () => {
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      const slug = await generateSlugViaLLM({
+        sessionContent: "Test content",
+        cfg,
+      });
+
+      expect(slug).toBeNull();
+    });
+
+    it("returns null when LLM returns empty text", async () => {
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      const slug = await generateSlugViaLLM({
+        sessionContent: "Test content",
+        cfg,
+      });
+
+      expect(slug).toBeNull();
+    });
+
+    it("returns null when embedded agent throws error", async () => {
+      const cfg: OpenClawConfig = {};
+
+      runEmbeddedPiAgentMock.mockRejectedValue(new Error("LLM timeout"));
+
+      const slug = await generateSlugViaLLM({
+        sessionContent: "Test content",
+        cfg,
+      });
+
+      expect(slug).toBeNull();
+    });
+  });
+
+  describe("embedded agent parameters", () => {
+    it("passes correct parameters to runEmbeddedPiAgent", async () => {
+      const cfg: OpenClawConfig = {
+        agents: {
+          defaults: {
+            model: {
+              primary: "anthropic/claude-sonnet-4-5",
+            },
+          },
+        },
+      };
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "test-slug" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      await generateSlugViaLLM({
+        sessionContent: "Testing parameters",
+        cfg,
+      });
+
+      expect(runEmbeddedPiAgentMock).toHaveBeenCalledTimes(1);
+      const callArgs = runEmbeddedPiAgentMock.mock.calls[0]?.[0];
+
+      // Verify all expected parameters are present
+      expect(callArgs).toMatchObject({
+        config: cfg,
+        provider: "anthropic",
+        model: "claude-sonnet-4-5",
+        timeoutMs: 15_000,
+      });
+
+      // Verify prompt includes session content
+      expect(callArgs?.prompt).toContain("Testing parameters");
+      expect(callArgs?.prompt).toContain("1-2 word filename slug");
+
+      // Verify session parameters
+      expect(callArgs?.sessionId).toMatch(/^slug-generator-\d+$/);
+      expect(callArgs?.sessionKey).toBe("temp:slug-generator");
+      expect(callArgs?.runId).toMatch(/^slug-gen-\d+$/);
+
+      // Verify temp session file path
+      expect(callArgs?.sessionFile).toContain("openclaw-slug-");
+      expect(callArgs?.sessionFile).toContain("session.jsonl");
+    });
+
+    it("truncates session content to 2000 characters in prompt", async () => {
+      const cfg: OpenClawConfig = {};
+      const longContent = "a".repeat(3000);
+
+      runEmbeddedPiAgentMock.mockResolvedValue({
+        payloads: [{ text: "truncated-slug" }],
+        meta: { runId: "test-run", sessionId: "test-session" },
+      });
+
+      await generateSlugViaLLM({
+        sessionContent: longContent,
+        cfg,
+      });
+
+      const callArgs = runEmbeddedPiAgentMock.mock.calls[0]?.[0];
+      const promptContentMatch = callArgs?.prompt.match(
+        /Conversation summary:\n([\s\S]+)\n\nReply/,
+      );
+      const extractedContent = promptContentMatch?.[1] ?? "";
+
+      expect(extractedContent.length).toBeLessThanOrEqual(2000);
+    });
+  });
+});