packages/mosaic/framework/tools/lease-broker/activation_version_gate.py

@@ -62,7 +62,14 @@ EXPECTED_ACTIVATION_CAPABILITY: Final[ActivationCapability] = {
 # capability as compact JSON.
 LEASE_CAPABILITY_PROBE_COMMAND: Final = "__lease-capability"
 
-PROBE_TIMEOUT_SECONDS: Final = 2.0
+# Budget for the out-of-process `mosaic __lease-capability` probe. The CLI
+# is a Node program whose cold start alone measures 2.2-2.3s on a mid-range
+# workstation (sb-it-1-dt, 2026-08-13), so a 2s budget made every launch on
+# such hosts fail closed with the #869 skew message even though the
+# capability matched. The timeout only bounds the pathological hang case —
+# the happy path returns as soon as the probe exits — so a generous budget
+# costs nothing on healthy hosts.
+PROBE_TIMEOUT_SECONDS: Final = 10.0
 
 # Override hook: a full shell-style command line (parsed with `shlex.split`)
 # to run INSTEAD of resolving `mosaic` on PATH and appending the probe
@@ -88,7 +95,13 @@ def _resolve_probe_command(environ: Mapping[str, str]) -> list[str] | None:
     if override:
         parsed = shlex.split(override)
         return parsed or None
-    resolved = shutil.which("mosaic")
+    # Resolve against the PROVIDED environment's PATH, not the ambient
+    # os.environ. Before this, a test passing a hermetic environ still
+    # resolved (and spawned) the host's real `mosaic` — masked only on hosts
+    # where the real probe happened to exceed the old 2s timeout. No PATH in
+    # the provided environment means nothing is resolvable (fail-closed),
+    # matching the probe's overall contract.
+    resolved = shutil.which("mosaic", path=environ.get("PATH", ""))
     if resolved is None:
         return None
     return [resolved, LEASE_CAPABILITY_PROBE_COMMAND]

packages/mosaic/src/commands/lease-activation-probe.ts

@@ -55,6 +55,19 @@ export const LEASE_ACTIVATION_CAPABILITY: LeaseActivationCapability = {
 /** Hidden CLI probe subcommand name — wired via {@link registerLeaseCapabilityProbe}. */
 export const LEASE_CAPABILITY_PROBE_COMMAND = '__lease-capability';
 
+/**
+ * Budget for the out-of-process capability probe. The probe launches a fresh
+ * Node process on the built CLI entrypoint, whose cold start alone measures
+ * 2.2-2.3s on a mid-range workstation (sb-it-1-dt, 2026-08-13) — so the
+ * previous 2s budget made the probe time out and report NO capability on
+ * such hosts, failing every launch with the #869 skew message even though
+ * the capability matched. The timeout only bounds the pathological hang
+ * case; the happy path returns as soon as the probe exits. Mirrors
+ * PROBE_TIMEOUT_SECONDS in the enforcement half
+ * (framework/tools/lease-broker/activation_version_gate.py).
+ */
+export const LEASE_CAPABILITY_PROBE_TIMEOUT_MS = 10_000;
+
 function capabilityMatches(candidate: LeaseActivationCapability | null): boolean {
   return (
     candidate !== null &&
@@ -141,7 +154,7 @@ export function defaultCapabilityProbe(
 
     const output = execFileSync(process.execPath, [cliEntry, LEASE_CAPABILITY_PROBE_COMMAND], {
       encoding: 'utf-8',
-      timeout: 2000,
+      timeout: LEASE_CAPABILITY_PROBE_TIMEOUT_MS,
       stdio: ['ignore', 'pipe', 'ignore'],
     });