feat(webapp): expose debounce fast-path/quantization knobs as env vars

Per Devin Review: the previous PR threaded only `useReplicaForFastPathRead`
from the env. `quantizeNewDelayUntilMs` and `fastPathSkipEnabled` were
hardcoded to their RunEngine defaults, so operators couldn't tune or
disable them without a code change.

Adds:
- `RUN_ENGINE_DEBOUNCE_QUANTIZE_NEW_DELAY_UNTIL_MS` (default 1000ms, 0 to
  disable)
- `RUN_ENGINE_DEBOUNCE_FAST_PATH_SKIP_ENABLED` (default "1", set to "0"
  as a kill-switch if the fast-path needs to be disabled in production
  without a redeploy)

Co-Authored-By: Eric Allam <eallam@icloud.com>

Author: devin-ai-integration[bot]

apps/webapp/app/env.server.ts

@@ -666,6 +666,21 @@ const EnvironmentSchema = z
       .int()
       .default(60_000 * 60), // 1 hour
 
+    /**
+     * Bucket size in milliseconds used to quantize the newly computed `delayUntil`
+     * in the debounce system. Quantization collapses concurrent triggers on the
+     * same hot debounce key onto the same target time so the unlocked fast-path
+     * skip is effective. Set to 0 to disable. Default: 1000ms (1s).
+     */
+    RUN_ENGINE_DEBOUNCE_QUANTIZE_NEW_DELAY_UNTIL_MS: z.coerce.number().int().min(0).default(1000),
+
+    /**
+     * Whether the unlocked fast-path skip is enabled in the debounce system.
+     * Acts as a kill switch in case the fast-path needs to be disabled in
+     * production without a redeploy. Default: "1" (enabled).
+     */
+    RUN_ENGINE_DEBOUNCE_FAST_PATH_SKIP_ENABLED: z.string().default("1"),
+
     RUN_ENGINE_WORKER_REDIS_HOST: z
       .string()
       .optional()

apps/webapp/app/v3/runEngine.server.ts

@@ -214,6 +214,8 @@ function createRunEngine() {
     // Debounce configuration
     debounce: {
       maxDebounceDurationMs: env.RUN_ENGINE_MAXIMUM_DEBOUNCE_DURATION_MS,
+      quantizeNewDelayUntilMs: env.RUN_ENGINE_DEBOUNCE_QUANTIZE_NEW_DELAY_UNTIL_MS,
+      fastPathSkipEnabled: env.RUN_ENGINE_DEBOUNCE_FAST_PATH_SKIP_ENABLED === "1",
       useReplicaForFastPathRead: env.RUN_ENGINE_DEBOUNCE_USE_REPLICA_FOR_FAST_PATH_READ === "1",
     },
   });