diff --git a/src/server/execute.test.ts b/src/server/execute.test.ts
new file mode 100644
index 0000000..24e924a
--- /dev/null
+++ b/src/server/execute.test.ts
@@ -0,0 +1,108 @@
+import { describe, it, expect } from "vitest";
+import { isK8s404, buildPartialRunError } from "./execute.js";
+
+describe("isK8s404", () => {
+  it("returns false for non-Error values", () => {
+    expect(isK8s404(null)).toBe(false);
+    expect(isK8s404(undefined)).toBe(false);
+    expect(isK8s404("string error")).toBe(false);
+    expect(isK8s404(404)).toBe(false);
+  });
+
+  it("returns false for unrelated errors", () => {
+    expect(isK8s404(new Error("something went wrong"))).toBe(false);
+    expect(isK8s404(new Error("HTTP-Code: 500 Message: Internal Server Error"))).toBe(false);
+  });
+
+  it("detects 404 from v1.0+ message format", () => {
+    const err = new Error("HTTP-Code: 404 Message: Unknown API Status Code! Body: ...");
+    expect(isK8s404(err)).toBe(true);
+  });
+
+  it("detects 404 from v0.x response.statusCode", () => {
+    const err = Object.assign(new Error("Not Found"), {
+      response: { statusCode: 404 },
+    });
+    expect(isK8s404(err)).toBe(true);
+  });
+
+  it("detects 404 from v1.0+ response.status", () => {
+    const err = Object.assign(new Error("Not Found"), {
+      response: { status: 404 },
+    });
+    expect(isK8s404(err)).toBe(true);
+  });
+
+  it("detects 404 from direct statusCode property", () => {
+    const err = Object.assign(new Error("Not Found"), { statusCode: 404 });
+    expect(isK8s404(err)).toBe(true);
+  });
+
+  it("does not match non-404 status codes on response", () => {
+    const err = Object.assign(new Error("Forbidden"), {
+      response: { statusCode: 403 },
+    });
+    expect(isK8s404(err)).toBe(false);
+  });
+});
+
+describe("buildPartialRunError", () => {
+  const initLine = JSON.stringify({
+    type: "system",
+    subtype: "init",
+    model: "claude-sonnet-4-6",
+    session_id: "sess_abc",
+  });
+
+  it("returns parse-failure message when exitCode is 0", () => {
+    expect(buildPartialRunError(0, "", "")).toBe("Failed to parse Claude JSON output");
+    expect(buildPartialRunError(0, "claude-sonnet-4-6", initLine)).toBe(
+      "Failed to parse Claude JSON output",
+    );
+  });
+
+  it("returns generic exit message when stdout is empty", () => {
+    expect(buildPartialRunError(1, "", "")).toBe("Claude exited with code 1");
+    expect(buildPartialRunError(null, "", "")).toBe("Claude exited with code -1");
+  });
+
+  it("skips system/init events and returns generic message when only init captured", () => {
+    const msg = buildPartialRunError(1, "claude-sonnet-4-6", initLine);
+    expect(msg).toBe(
+      "Claude started but did not produce a result (model: claude-sonnet-4-6) — check API credentials, model support, and adapter config",
+    );
+  });
+
+  it("includes model from parsedStream when stdout is init-only", () => {
+    const msg = buildPartialRunError(null, "MiniMax-M2.7", initLine);
+    expect(msg).toContain("MiniMax-M2.7");
+    expect(msg).not.toContain("type");
+    expect(msg).not.toContain("system");
+  });
+
+  it("uses first non-system line as content when present", () => {
+    const stdout = [initLine, "Error: no API key configured"].join("\n");
+    const msg = buildPartialRunError(1, "claude-sonnet-4-6", stdout);
+    expect(msg).toBe("Claude exited with code 1: Error: no API key configured");
+  });
+
+  it("uses first non-system JSON event as content", () => {
+    const resultLike = JSON.stringify({ type: "result", subtype: "error", result: "rate limit" });
+    const stdout = [initLine, resultLike].join("\n");
+    const msg = buildPartialRunError(2, "claude-sonnet-4-6", stdout);
+    expect(msg).toContain("rate limit");
+    expect(msg).toContain("code 2");
+  });
+
+  it("null exitCode renders as -1 in message", () => {
+    const msg = buildPartialRunError(null, "", "Some plain error text");
+    expect(msg).toBe("Claude exited with code -1: Some plain error text");
+  });
+
+  it("skips multiple consecutive system events", () => {
+    const anotherSystem = JSON.stringify({ type: "system", subtype: "other" });
+    const stdout = [initLine, anotherSystem, "real error line"].join("\n");
+    const msg = buildPartialRunError(1, "model-x", stdout);
+    expect(msg).toBe("Claude exited with code 1: real error line");
+  });
+});
diff --git a/src/server/execute.ts b/src/server/execute.ts
index c313f15..ea8c282 100644
--- a/src/server/execute.ts
+++ b/src/server/execute.ts
@@ -19,8 +19,9 @@ const MAX_LOG_RECONNECT_ATTEMPTS = 50;
 /**
  * Detect a Kubernetes 404 (Not Found) error from @kubernetes/client-node.
  * Works for both v0.x (response.statusCode) and v1.0+ (response.status, message).
+ * Exported for unit tests.
  */
-function isK8s404(err: unknown): boolean {
+export function isK8s404(err: unknown): boolean {
   if (!(err instanceof Error)) return false;
   const e = err as unknown as Record<string, unknown>;
   const resp = e.response as Record<string, unknown> | undefined;
@@ -29,6 +30,45 @@ function isK8s404(err: unknown): boolean {
   return /HTTP-Code:\s*404\b/.test(err.message);
 }
 
+/**
+ * Build the error message when Claude's stdout contains no result event.
+ * Skips system/init event lines so the UI doesn't display the raw init JSON.
+ * Exported for unit tests.
+ */
+export function buildPartialRunError(
+  exitCode: number | null,
+  model: string,
+  stdout: string,
+): string {
+  if (exitCode === 0) return "Failed to parse Claude JSON output";
+
+  // Walk stdout lines, skip system events, return the first real content line.
+  const firstContentLine = stdout.split(/\r?\n/)
+    .map((l) => l.trim())
+    .find((l) => {
+      if (!l) return false;
+      try {
+        const obj = JSON.parse(l);
+        if (typeof obj === "object" && obj !== null && (obj as Record<string, unknown>).type === "system") return false;
+      } catch {
+        // not JSON — treat as content
+      }
+      return true;
+    }) ?? "";
+
+  // If we only have system/init events and nothing else, surface the model
+  // name so the operator can diagnose missing credentials or unsupported model.
+  const initOnlyOutput = stdout.trim() !== "" && model !== "" && !firstContentLine;
+  if (initOnlyOutput) {
+    const modelHint = model ? ` (model: ${model})` : "";
+    return `Claude started but did not produce a result${modelHint} — check API credentials, model support, and adapter config`;
+  }
+
+  return firstContentLine
+    ? `Claude exited with code ${exitCode ?? -1}: ${firstContentLine}`
+    : `Claude exited with code ${exitCode ?? -1}`;
+}
+
 /**
  * Wait for the Job's pod to reach a terminal or running state.
  * Returns the pod name once logs can be streamed, or throws on failure.
@@ -640,13 +680,27 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
       stdout = logResult.value;
     }
 
-    // If the follow stream missed output (container exited quickly), do a
-    // one-shot log read as fallback before the pod is cleaned up.
-    if (!stdout.trim()) {
-      await onLog("stdout", `[paperclip] Log stream returned empty — reading pod logs directly...\n`);
-      stdout = await readPodLogs(namespace, podName, kubeconfigPath);
-      if (stdout.trim()) {
+    // One-shot log fallback: handles two failure modes with a single read.
+    // Mode 1 — empty stream: the follow stream returned nothing (fast exit before connection).
+    // Mode 2 — partial stream: we have some output but no result event (follow stream raced
+    //   with container exit and captured only the init line before the connection dropped).
+    // A one-shot readPodLogs is more reliable for already-terminated containers and reads
+    // from the beginning of the log, giving us the full output.
+    // We use a cheap string scan for the result-event guard (avoids a full JSON parse here;
+    // the authoritative parse happens once below after all fallbacks complete).
+    const hasResultEvent = stdout.includes('"type":"result"');
+    const needsOneShot = !stdout.trim() || (stdout.trim() && !hasResultEvent);
+    if (needsOneShot) {
+      if (!stdout.trim()) {
+        await onLog("stdout", `[paperclip] Log stream returned empty — reading pod logs directly...\n`);
+      }
+      const oneShotLogs = await readPodLogs(namespace, podName, kubeconfigPath);
+      if (!stdout.trim() && oneShotLogs.trim()) {
+        stdout = oneShotLogs;
         await onLog("stdout", stdout);
+      } else if (oneShotLogs && oneShotLogs.length > stdout.length) {
+        await onLog("stdout", `[paperclip] Log stream captured partial output — supplemental one-shot read returned more content.\n`);
+        stdout = oneShotLogs;
       }
     }
 
@@ -739,16 +793,11 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
   }
 
   if (!parsed) {
-    const stderrLine = stdout.split(/\r?\n/).map((l) => l.trim()).find(Boolean) ?? "";
     return {
       exitCode,
       signal: null,
       timedOut: false,
-      errorMessage: exitCode === 0
-        ? "Failed to parse Claude JSON output"
-        : stderrLine
-          ? `Claude exited with code ${exitCode ?? -1}: ${stderrLine}`
-          : `Claude exited with code ${exitCode ?? -1}`,
+      errorMessage: buildPartialRunError(exitCode, parsedStream.model, stdout),
       resultJson: { stdout },
     };
   }