perf(wsl): release environment probe deadline timers

src/main/wsl/wsl-guest-environment.test.ts

@@ -58,6 +58,33 @@ describe('probing', () => {
     await getWslGuestEnvironment('Debian')
     expect(runProcessMock).toHaveBeenCalledTimes(2)
   })
+
+  it('does not retain deadline timers after a concurrent probe settles', async () => {
+    vi.useFakeTimers()
+    try {
+      respondWithPayload(GOOD)
+      await Promise.all(Array.from({ length: 32 }, () => getWslGuestEnvironment('Ubuntu')))
+      expect(vi.getTimerCount()).toBe(0)
+      expect(runProcessMock).toHaveBeenCalledTimes(1)
+    } finally {
+      vi.useRealTimers()
+    }
+  })
+
+  it('reads a warm cache without allocating deadline timers', async () => {
+    respondWithPayload(GOOD)
+    const environment = await getWslGuestEnvironment('Ubuntu')
+    const timeout = vi.spyOn(globalThis, 'setTimeout')
+    try {
+      for (let index = 0; index < 100; index++) {
+        expect(await getWslGuestEnvironment('Ubuntu')).toBe(environment)
+      }
+      expect(timeout).not.toHaveBeenCalled()
+      expect(runProcessMock).toHaveBeenCalledTimes(1)
+    } finally {
+      timeout.mockRestore()
+    }
+  })
 })
 
 describe('bad answers are not cached as good ones', () => {

src/main/wsl/wsl-guest-environment.ts

@@ -125,6 +125,10 @@ export function getWslGuestEnvironment(
   budgetMs = PROBE_TIMEOUT_MS
 ): Promise<WslGuestEnvironment | null> {
   const key = cacheKey(distro)
+  const cached = resolved.get(key)
+  if (cached) {
+    return Promise.resolve(cached)
+  }
   const retry = retryAfter.get(key)
   if (retry !== undefined && Date.now() >= retry) {
     inFlight.delete(key)
@@ -154,13 +158,14 @@ export function getWslGuestEnvironment(
     // Why race: joining an in-flight probe used to mean waiting out the
     // *starter's* budget, so a joiner could reach its own command with 1ms --
     // the exact hazard the budget plumbing was added to remove.
+    let timer: ReturnType<typeof setTimeout>
     return Promise.race([
       existing,
       new Promise<null>((resolve) => {
-        const timer = setTimeout(() => resolve(null), budgetMs)
+        timer = setTimeout(() => resolve(null), budgetMs)
         timer.unref?.()
       })
-    ])
+    ]).finally(() => clearTimeout(timer))
   }
   // Store before awaiting so a burst collapses into one probe.
   // Why catch: runProcess REJECTS when the child cannot be started (ENOENT on a