fix(webchat): suppress NO_REPLY token in chat transcript rendering (#32183)

* fix(types): resolve pre-existing TS errors in agent-components and pairing-store

- agent-components.ts: normalizeDiscordAllowList returns {allowAll, ids, names},
  not an array — use ids.values().next().value instead of [0] indexing
- pairing-store.ts: add non-null assertions for stat after cache-miss guard
  (resolveAllowFromReadCacheOrMissing returns early when stat is null)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(webchat): suppress NO_REPLY token in chat transcript rendering

Filter assistant NO_REPLY-only entries from chat.history responses at
the gateway API boundary and add client-side defense-in-depth guards in
the UI chat controller so internal silent tokens never render as visible
chat bubbles.

Two-layer fix:
1. Gateway: extractAssistantTextForSilentCheck + isSilentReplyText
   filter in sanitizeChatHistoryMessages (entry.text takes precedence
   over entry.content to avoid dropping messages with real text)
2. UI: isAssistantSilentReply + isSilentReplyStream guards on all 5
   message insertion points in handleChatEvent and loadChatHistory

Fixes #32015

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(webchat): align isAssistantSilentReply text/content precedence with gateway

* webchat: tighten NO_REPLY transcript and delta filtering

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/pairing/pairing-store.ts

@@ -374,10 +374,11 @@ async function readAllowFromStateForPathWithExists(
     allowFrom: [],
   });
   const entries = normalizeAllowFromList(channel, value);
+  // stat is guaranteed non-null here: resolveAllowFromReadCacheOrMissing returns early when stat is null.
   setAllowFromReadCache(filePath, {
     exists,
-    mtimeMs: stat.mtimeMs,
-    size: stat.size,
+    mtimeMs: stat!.mtimeMs,
+    size: stat!.size,
     entries,
   });
   return { entries, exists };
@@ -419,13 +420,14 @@ function readAllowFromStateForPathSyncWithExists(
     }
     return { entries: [], exists: false };
   }
+  // stat is guaranteed non-null here: resolveAllowFromReadCacheOrMissing returns early when stat is null.
   try {
     const parsed = JSON.parse(raw) as AllowFromStore;
     const entries = normalizeAllowFromList(channel, parsed);
     setAllowFromReadCache(filePath, {
       exists: true,
-      mtimeMs: stat.mtimeMs,
-      size: stat.size,
+      mtimeMs: stat!.mtimeMs,
+      size: stat!.size,
       entries,
     });
     return { entries, exists: true };
@@ -433,8 +435,8 @@ function readAllowFromStateForPathSyncWithExists(
     // Keep parity with async reads: malformed JSON still means the file exists.
     setAllowFromReadCache(filePath, {
       exists: true,
-      mtimeMs: stat.mtimeMs,
-      size: stat.size,
+      mtimeMs: stat!.mtimeMs,
+      size: stat!.size,
       entries: [],
     });
     return { entries: [], exists: true };