docs: scheduled-discovery env + single-replica constraint; VISION gate-clock reset

homelab-integration.md gains a "Scheduled discovery" section documenting
TAPIR_DISCOVERY_INTERVAL and TAPIR_FETCH_RATE and the load-bearing
single-replica constraint (in-process scheduler → replicas: 1 is required;
>1 double-runs discovery). VISION Stage 0 carries a pointer to ADR-018's
gate-clock reset so nothing in docs implies the window started before
unprompted use was possible.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

VISION.md

@@ -90,6 +90,11 @@ to the next stage's ambition until the current stage's test passes.
   table (see infra/Tapir build) answers "returned/read in ≥2 distinct weeks" even without an
   action click — the honest signal for a *reading* product. Login events accrue only from their
   deploy date onward, so the gate window's data begins then.
+- **Gate-clock reset (ADR-018).** The 3–4 week window starts when in-process scheduled discovery
+  + auto-summarize ship — before that, unprompted use was impossible, so the prior window
+  measured nothing (this is starting the clock when the experiment can actually run, not a reset
+  to dodge a failing gate). The 2026-07-01 check-in referenced above moves accordingly to ~3–4
+  weeks after this deploys. See DECISIONS.md ADR-018.
 - **This is the gate.** Hardening (Stage 1) and any SaaS ambition stay deferred until this
   behavioural signal exists. Note: multi-user machinery was deliberately built *ahead* of
   this gate (ADR-012) with isolation enforced — that was an explicit, recorded call, not a