feat(vision-manager): memory-pressure yield gate (+ retain analysis gate) (#8)

.env.example

@@ -218,3 +218,15 @@ VISION_MANAGER_DATABASE_URL=
 # VISION_START_HEALTH_TIMEOUT  Max seconds to wait for /health 200 after start. Default 300 (cold model load).
 # VISION_RESPECT_CRAWL_MUTEX   1 = don't start vision while a crawl runs (RAM mutex on the 8 GiB box). Default 1.
 # VISION_MAX_UPTIME         >0 = force-stop vision after N seconds running (backstop). Default 0 (disabled).
+#
+# Memory-pressure yield — the dynamic generalization of the crawl mutex. The
+# manager reads host-wide used% (from /proc/meminfo MemAvailable) and stops a
+# RUNNING vision when memory gets tight, so a spike elsewhere (a crawl, CI, a
+# backend burst) can finish instead of the kernel OOM-killer shooting something
+# stateful. Two watermarks give hysteresis; the cooldown prevents stop/restart
+# thrash when vision itself is the hog. See VISION-MEMORY-YIELD.md.
+# VISION_MEM_YIELD_ENABLED      1 = enable the gate, 0 = disable entirely. Default 1.
+# VISION_MEM_HIGH_WATERMARK_PCT used% >= this → actively stop a running vision. Default 92.
+# VISION_MEM_LOW_WATERMARK_PCT  used% >= this → inhibit starts (keep HIGH - LOW >= ~10 so the band beats jitter). Default 80.
+# VISION_MEM_YIELD_COOLDOWN     Seconds after a pressure-stop during which restart is refused regardless of backlog. Default 300.
+# VISION_MEM_POLL_INTERVAL      Mem sub-poll cadence, seconds (<= VISION_POLL_INTERVAL); catches spikes between backlog ticks. Default 5.