Address remaining review items: Synapse caching, cycle detection, cache/ratelimit/kanban

- SynapseHelper: memoize username->Matrix-ID lookups per-request (incl. negative
  results) and add an overall time budget to resolveUsernames() plus a 2s connect
  timeout, so notifying N watchers with a slow/unreachable Synapse can't stall the
  request for N x 5s. (Chosen over async/queue per maintainer.)
- DependencyModel: fix cycle detection treating 'blocks' and 'blocked_by' as the
  same edge direction. They are inverse relationships (single row each, no mirror
  row), so the traversal now walks a unified precedence graph (blocks: ticket->
  depends_on; blocked_by: depends_on->ticket) and wouldCreateCycle normalizes the
  new edge's direction. Prevents both false-positive and missed cycles.
- CacheHelper: anchor prefix-delete to exact key boundaries (bare prefix or
  prefix + '_' + md5) so delete('workflow') can't wipe a 'workflow_rules' cache.
- RateLimitMiddleware: hold an exclusive flock across the per-IP counter's
  read-modify-write so concurrent requests can't both read N and write N+1
  (undercounting past the limit). Fails open if the file can't be locked.
- dashboard.js: kanban status update now uses lt.api.post (per no-raw-fetch
  convention) and reverts the card AND the optimistic column counts on failure
  (the old raw-fetch catch left the card moved without reverting).
- BulkOperationsModel: document that bulk_status/bulk_close intentionally bypass
  workflow transition validation (admin override, by design).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

helpers/SynapseHelper.php

@@ -4,8 +4,9 @@
  * SynapseHelper
  *
  * Resolves local (SSO) usernames → Matrix user IDs by querying the
- * Synapse Admin REST API directly.  No caching — every call is live
- * so results never go stale.
+ * Synapse Admin REST API directly. Results are memoized per-request (not
+ * across requests, so they don't go stale between requests), and a batch
+ * resolve has an overall time budget to bound request latency.
  *
  * Required config (.env) keys:
  *   MATRIX_DOMAIN      e.g. matrix.lotusguild.org
@@ -14,6 +15,12 @@
  */
 class SynapseHelper
 {
+    /** Per-request memo of username => Matrix ID|null, so repeat watchers are free. */
+    private static array $cache = [];
+
+    /** Total wall-clock budget (seconds) for a single resolveUsernames() batch. */
+    private const RESOLVE_BUDGET_SECONDS = 5;
+
     /**
      * Resolve a local SSO username to its Matrix user ID.
      *
@@ -29,6 +36,11 @@ class SynapseHelper
      */
     public static function resolveUsername(string $username): ?string
     {
+        // Serve from the per-request cache when we've already looked this up.
+        if (array_key_exists($username, self::$cache)) {
+            return self::$cache[$username];
+        }
+
         $baseUrl = $GLOBALS['config']['SYNAPSE_ADMIN_URL']  ?? null;
         $token   = $GLOBALS['config']['SYNAPSE_ADMIN_TOKEN'] ?? null;
         $domain  = $GLOBALS['config']['MATRIX_DOMAIN']      ?? null;
@@ -49,6 +61,7 @@ class SynapseHelper
             'Accept: application/json',
         ]);
         curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
+        curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 2); // fail fast when Synapse is unreachable
         curl_setopt($ch, CURLOPT_TIMEOUT, 5);
 
         $body      = curl_exec($ch);
@@ -56,25 +69,24 @@ class SynapseHelper
         $curlError = curl_error($ch);
         curl_close($ch);
 
+        $resolved = null;
         if ($curlError) {
             error_log("SynapseHelper: cURL error resolving '{$username}': {$curlError}");
-            return null;
-        }
-
-        if ($httpCode === 200) {
+        } elseif ($httpCode === 200) {
             $data = json_decode($body, true);
             // Confirm the response contains the name we expect
             if (!empty($data['name'])) {
-                return $data['name']; // e.g. "@jared:matrix.lotusguild.org"
+                $resolved = $data['name']; // e.g. "@jared:matrix.lotusguild.org"
             }
-        }
-
-        // 404 = user not found in Synapse; other codes = error
-        if ($httpCode !== 404) {
+        } elseif ($httpCode !== 404) {
+            // 404 = user not found in Synapse; other codes = error
             error_log("SynapseHelper: unexpected HTTP {$httpCode} resolving '{$username}'");
         }
 
-        return null;
+        // Memoize for the rest of this request (including negative results, so a
+        // missing/unreachable user isn't retried within the same request).
+        self::$cache[$username] = $resolved;
+        return $resolved;
     }
 
     /**
@@ -87,7 +99,16 @@ class SynapseHelper
     public static function resolveUsernames(array $usernames): array
     {
         $ids = [];
+        $deadline = microtime(true) + self::RESOLVE_BUDGET_SECONDS;
         foreach ($usernames as $username) {
+            // Cached lookups are free and always allowed; for uncached ones, stop
+            // making live calls once the batch budget is spent so a slow/unreachable
+            // Synapse can't stall the request for N × per-call timeout.
+            $cached = array_key_exists($username, self::$cache);
+            if (!$cached && microtime(true) >= $deadline) {
+                error_log('SynapseHelper: resolve budget exhausted; skipping remaining lookups');
+                break;
+            }
             $id = self::resolveUsername($username);
             if ($id !== null) {
                 $ids[] = $id;