feat(runtime): add integration hardening and diagnostics

docs/RESOURCE_BUDGET.md

@@ -0,0 +1,45 @@
+# Runtime resource budget
+
+Milestone 010 fixes and exposes the following production limits. They are
+compile-time bounds, not targets that may grow with match duration.
+
+| Resource | Limit | Defensive behavior |
+| --- | ---: | --- |
+| WebSocket connections | 6 | A seventh WebSocket handshake is rejected. |
+| LwIP sockets | 16 | ESP-IDF remains configured by `sdkconfig.defaults`. |
+| Client message | 512 bytes | An oversized frame is counted and disconnected. |
+| Outgoing message | 768 bytes | An over-limit message cannot enter the queue. |
+| Outgoing queue | 12 entries | Queue overflow is counted; memory cannot grow. |
+| Game command queue | 16 entries | Excess commands receive `queue_full`. |
+| Input rate | 20 messages/second | Excess messages are rejected; sustained abuse above 40 in the same window is disconnected. |
+| Player response budget | 250 ms | The physical stress client fails above this round-trip threshold. |
+| Observer update policy | Latest bounded projection | A busy observer may lose intermediate dynamic chunks and recover on a newer projection. Failed or stalled required sends close the socket. |
+| Reconnect deadline | 60,000 ms | Gameplay pauses, then ends in a draw at expiry. |
+
+## Build-time measurements
+
+The Milestone 010 production build on 2026-09-05 reported 124,276 of 327,680
+static RAM bytes and 1,028,600 of 2,097,152 application bytes. The independent
+binary check measured 1,029,232 bytes in the 2 MiB factory partition, leaving
+1,067,920 bytes of application margin. The compressed web
+payload totals 19,253 bytes against its 1.5 MiB budget, leaving 1,553,611 bytes
+of payload margin. LittleFS remains the fixed 1,984 KiB partition and its image
+is checked against `partitions.csv` on every build.
+
+The global authoritative gateway, including its one maze, one projection
+buffer, fixed queues, sessions, timers, and metrics, occupies 86,840 bytes of
+static storage in the production ELF. It does not allocate a maze or
+projection per client. No production source or test requires PSRAM or a GPIO.
+
+## Runtime measurements
+
+`GET /diagnostics` returns current and minimum internal 8-bit heap values and
+the largest internal free block. It deliberately samples
+`MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT`, so external RAM cannot make a failing
+internal-memory result appear healthy. Serial samples use the same capability
+mask.
+
+Final six-client, slow-client, repeated-match, and network-recovery samples
+belong in the active milestone evidence in `PLANS.md`. Build-time numbers in
+this document must be refreshed if the production image changes before that
+evidence is recorded.