feat(intake-links): per-(link, project) cap read/write

Phase 9a Task 3. isLinkProjectUsable reads today's counter (or
treats no row as 0). bumpDailyCapForProject upserts via the unique
(link, project, date) index. The Phase 8 helpers stay live for the
old shape; Phase 9b's wizard picks which one to call based on
whether the link is per-project (Phase 8) or per-client (Phase 9).

src/lib/intake-links/index.ts

@@ -1,7 +1,16 @@
 import "server-only";
 
 import { getAdminPb } from "@/lib/pb/admin";
-import type { IntakeLinkRecord } from "@/lib/pb/types";
+import type {
+  IntakeLinkRecord,
+  IntakeLinkSubmissionRecord,
+} from "@/lib/pb/types";
+import {
+  computeDateForCounter,
+  defaultCapFor,
+  isDailyCapReached,
+  nextCount,
+} from "@/lib/intake-links/submissions";
 
 const DEFAULT_DAILY_CAP = 100;
 
@@ -102,3 +111,69 @@ export async function bumpSubmissionCount(link: IntakeLinkRecord): Promise<void>
     last_submission_at: new Date().toISOString(),
   });
 }
+
+/**
+ * Phase 9: True when the (link, project) pair is still usable right now.
+ *
+ * Reads today's counter from the new `intake_link_submissions` collection.
+ * On any DB read error, returns false — Phase 8 used the same conservative
+ * default (a flaky read fails closed, never open).
+ */
+export async function isLinkProjectUsable(
+  link: IntakeLinkRecord,
+  projectId: string,
+  now: Date = new Date()
+): Promise<boolean> {
+  if (!link.active) return false;
+  if (link.expires_at) {
+    const expiry = link.expires_at.slice(0, 10);
+    if (computeDateForCounter(now) > expiry) return false;
+  }
+  const cap = defaultCapFor(link.max_submissions_per_day);
+  const today = computeDateForCounter(now);
+
+  const pb = await getAdminPb();
+  try {
+    const row = await pb
+      .collection("intake_link_submissions")
+      .getFirstListItem<IntakeLinkSubmissionRecord>(
+        `link = "${link.id}" && project = "${projectId}" && date = "${today}"`
+      );
+    return !isDailyCapReached(row.count, cap);
+  } catch {
+    // No row for today → 0 submissions → below the cap (unless cap=0).
+    return !isDailyCapReached(0, cap);
+  }
+}
+
+/**
+ * Phase 9: Increment today's counter for the (link, project) pair.
+ *
+ * Uses the unique `(link, project, date)` index: a fresh row is created on
+ * first submission of the day, subsequent submissions update the count.
+ */
+export async function bumpDailyCapForProject(
+  link: IntakeLinkRecord,
+  projectId: string
+): Promise<void> {
+  const pb = await getAdminPb();
+  const today = computeDateForCounter();
+
+  try {
+    const existing = await pb
+      .collection("intake_link_submissions")
+      .getFirstListItem<IntakeLinkSubmissionRecord>(
+        `link = "${link.id}" && project = "${projectId}" && date = "${today}"`
+      );
+    await pb.collection("intake_link_submissions").update(existing.id, {
+      count: nextCount(existing.count),
+    });
+  } catch {
+    await pb.collection("intake_link_submissions").create({
+      link: link.id,
+      project: projectId,
+      date: today,
+      count: 1,
+    });
+  }
+}