chore(labs): tidy OCR capability enum, Fitbit key delimiter, Coach docblock

Drop the unreachable text-only-model reason from the OCR capability
enum and its DTO type. Replace the literal NUL delimiter in the Fitbit
dedup map keys with a named constant so text tooling stops treating the
file as binary (behaviour unchanged). Correct the Coach tool-executor
docblock, which overstated cross-tool snapshot-cache sharing.

src/app/api/labs/ocr/capability/route.ts

@@ -4,7 +4,7 @@
  * Cheap probe (no provider call) the Labs UI uses to decide whether to show
  * the "Scan a report" affordance. Returns `{ available, reason, pdfSupported }`
  * for the calling user's configured AI provider. The surface stays dark for
- * codex-only / text-only-model users.
+ * users with no provider configured and no local-OCR opt-in.
  */
 import { apiHandler, requireAuth } from "@/lib/api-handler";
 import { apiSuccess } from "@/lib/api-response";

src/lib/ai/coach/tools/executor.ts

@@ -20,8 +20,10 @@
  *     mutation or egress surface.
  *
  * The builder result is memoised by the 60s snapshot LRU keyed on
- * `(userId, window, sources)`, so several tool calls in one turn (and the
- * base-context inventory build) share the underlying reads.
+ * `(userId, window, sources)`. Each tool scopes to a different source set, so
+ * tool calls for distinct domains do NOT share a cache entry; sharing happens
+ * only when the SAME scope recurs (a repeated call, or a turn that re-enters
+ * the same domain) within the 60s window.
  */
 import { z } from "zod/v4";
 

src/lib/fitbit/sync.ts

@@ -47,6 +47,14 @@ import {
 /** Refresh the access token this many ms before `tokenExpiresAt`. */
 const TOKEN_REFRESH_BUFFER_MS = 5 * 60 * 1000;
 
+/**
+ * Delimiter joining `(type, externalId)` into a single dedup map key. A
+ * control character keeps it unambiguous against any value a real type or
+ * externalId could contain, while staying a normal printable-safe constant
+ * (a literal NUL in the source made text tooling treat the file as binary).
+ */
+const DEDUP_KEY_DELIM = "\u0000";
+
 /**
  * Overlap window for the incremental sync, in ms. Fitbit finalises daily
  * summaries after the fact (a daily SpO2 / HRV / RHR can settle hours after the
@@ -396,7 +404,10 @@ export async function upsertFitbitMeasurements(
     liveByKey = new Map(
       existing
         .filter((e) => e.externalId !== null)
-        .map((e) => [`${e.type}${e.externalId}`, { id: e.id }]),
+        .map((e) => [
+          `${e.type}${DEDUP_KEY_DELIM}${e.externalId}`,
+          { id: e.id },
+        ]),
     );
   } catch (err) {
     // A probe failure must not strand the whole batch; fall back to treating
@@ -421,7 +432,7 @@ export async function upsertFitbitMeasurements(
   const plannedCreateKeys = new Set<string>();
   for (const r of readings) {
     const type = r.type as MeasurementType;
-    const key = `${type}${r.externalId}`;
+    const key = `${type}${DEDUP_KEY_DELIM}${r.externalId}`;
     const live = liveByKey.get(key);
     if (live) {
       toUpdate.push({ id: live.id, r });
@@ -438,7 +449,9 @@ export async function upsertFitbitMeasurements(
     } else {
       // A duplicate fresh key inside the same batch — overwrite the planned
       // create's payload so last-write-wins, matching the prior upsert loop.
-      const idx = toCreate.findIndex((c) => `${c.type}${c.externalId}` === key);
+      const idx = toCreate.findIndex(
+        (c) => `${c.type}${DEDUP_KEY_DELIM}${c.externalId}` === key,
+      );
       if (idx >= 0) {
         toCreate[idx] = {
           type,

src/lib/openapi/routes/ocr.ts

@@ -29,9 +29,7 @@ const capabilityResponse = z
   .object({
     available: z.boolean(),
     mode: z.enum(["vision", "text"]).nullable(),
-    reason: z
-      .enum(["no-provider", "text-only-model", "enable-local-ocr"])
-      .nullable(),
+    reason: z.enum(["no-provider", "enable-local-ocr"]).nullable(),
     pdfSupported: z.boolean(),
   })
   .meta({

src/lib/validations/labs-ocr.ts

@@ -207,7 +207,7 @@ export interface OcrCapabilityDto {
    */
   mode: "vision" | "text" | null;
   /** Why scanning is unavailable, when it is. */
-  reason: "no-provider" | "text-only-model" | "enable-local-ocr" | null;
+  reason: "no-provider" | "enable-local-ocr" | null;
   /** Whether PDF uploads are accepted (Anthropic vision provider only). */
   pdfSupported: boolean;
 }