fix: cache ps output across sessions to fix 51s dashboard load (#244)

* fix: cache ps output across sessions to fix 51s dashboard load

findClaudeProcess() was calling `ps -eo pid,tty,args` once per session.
On machines with ~1150 processes, each `ps` call takes 30-35s. With 18
sessions enriched in parallel, this caused /api/sessions to take 51+
seconds despite the 2s per-session timeout.

Add a module-level TTL cache (5s) with in-flight deduplication so `ps`
is called at most once regardless of session count. Also reduce timeouts
from 30s to 5s — stale process data isn't useful.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: guard ps cache callbacks against stale overwrites

The .then() and catch callbacks in getCachedProcessList() could clobber
a newer in-flight cache entry if the TTL expired and a new request
replaced psCache while the old one was still pending. Both now check
`psCache?.promise === promise` before writing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/plugins/agent-claude-code/src/index.test.ts

@@ -30,7 +30,7 @@ vi.mock("node:os", () => ({
   homedir: mockHomedir,
 }));
 
-import { create, manifest, default as defaultExport } from "./index.js";
+import { create, manifest, default as defaultExport, resetPsCache } from "./index.js";
 
 // ---------------------------------------------------------------------------
 // Test helpers
@@ -108,6 +108,7 @@ function mockJsonlFiles(
 // ---------------------------------------------------------------------------
 beforeEach(() => {
   vi.clearAllMocks();
+  resetPsCache();
   mockHomedir.mockReturnValue("/mock/home");
 });
 

packages/plugins/agent-claude-code/src/index.ts

@@ -386,6 +386,55 @@ function extractCost(lines: JsonlLine[]): CostEstimate | undefined {
 // Process Detection
 // =============================================================================
 
+/**
+ * TTL cache for `ps -eo pid,tty,args` output. Without this, listing N sessions
+ * would spawn N concurrent `ps` processes, each taking 30+ seconds on machines
+ * with many processes. The cache ensures `ps` is called at most once per TTL
+ * window regardless of how many sessions are being enriched.
+ */
+let psCache: { output: string; timestamp: number; promise?: Promise<string> } | null = null;
+const PS_CACHE_TTL_MS = 5_000;
+
+/** Reset the ps cache. Exported for testing only. */
+export function resetPsCache(): void {
+  psCache = null;
+}
+
+async function getCachedProcessList(): Promise<string> {
+  const now = Date.now();
+  if (psCache && now - psCache.timestamp < PS_CACHE_TTL_MS) {
+    // Cache hit — return resolved output or wait for in-flight request
+    if (psCache.promise) return psCache.promise;
+    return psCache.output;
+  }
+
+  // Cache miss or expired — start a single `ps` call and share the promise.
+  // Guard both callbacks so they only update psCache if it still belongs to
+  // this request — a newer request may have replaced it while we were waiting.
+  const promise = execFileAsync("ps", ["-eo", "pid,tty,args"], {
+    timeout: 5_000,
+  }).then(({ stdout }) => {
+    if (psCache?.promise === promise) {
+      psCache = { output: stdout, timestamp: Date.now() };
+    }
+    return stdout;
+  });
+
+  // Store the in-flight promise so concurrent callers share it
+  psCache = { output: "", timestamp: now, promise };
+
+  try {
+    return await promise;
+  } catch {
+    // On failure, clear cache so the next caller retries — but only if
+    // psCache still points to this request (avoid clobbering a newer entry)
+    if (psCache?.promise === promise) {
+      psCache = null;
+    }
+    return "";
+  }
+}
+
 /**
  * Check if a process named "claude" is running in the given runtime handle's context.
  * Uses ps to find processes by TTY (for tmux) or by PID.
@@ -397,7 +446,7 @@ async function findClaudeProcess(handle: RuntimeHandle): Promise<number | null>
       const { stdout: ttyOut } = await execFileAsync(
         "tmux",
         ["list-panes", "-t", handle.id, "-F", "#{pane_tty}"],
-        { timeout: 30_000 },
+        { timeout: 5_000 },
       );
       // Iterate all pane TTYs (multi-pane sessions) — succeed on any match
       const ttys = ttyOut
@@ -407,12 +456,9 @@ async function findClaudeProcess(handle: RuntimeHandle): Promise<number | null>
         .filter(Boolean);
       if (ttys.length === 0) return null;
 
-      // Use `args` instead of `comm` so we can match the CLI name even when
-      // the process runs via a wrapper (e.g. node, python).  `comm` would
-      // report "node" instead of "claude" in those cases.
-      const { stdout: psOut } = await execFileAsync("ps", ["-eo", "pid,tty,args"], {
-        timeout: 30_000,
-      });
+      const psOut = await getCachedProcessList();
+      if (!psOut) return null;
+
       const ttySet = new Set(ttys.map((t) => t.replace(/^\/dev\//, "")));
       // Match "claude" as a word boundary — prevents false positives on
       // names like "claude-code" or paths that merely contain the substring.