fix: add type guards and null checks for UUID handling in snip functionality

- Add UUID type import and type guard in force-snip command
- Add null/undefined checks in snipCompact, snipProjection, and sessionStorage
- Improve optional chaining in SnipTool for safer property access
- Prevent potential runtime errors from invalid UUID values

Co-Authored-By: claude-sonnet-4-6 <noreply@anthropic.com>

packages/builtin-tools/src/tools/SnipTool/SnipTool.ts

@@ -79,13 +79,11 @@ Guidelines:
   },
 
   async call(input: SnipInput) {
-    // Snip implementation is handled by the query engine's projection system.
-    // The tool call itself records the intent; the query engine intercepts
-    // snip tool results and adjusts its message projection accordingly.
+    const ids = input?.message_ids ?? []
     return {
       data: {
-        snipped_count: input.message_ids.length,
-        summary: input.reason ?? `Snipped ${input.message_ids.length} messages`,
+        snipped_count: ids.length,
+        summary: input?.reason ?? `Snipped ${ids.length} messages`,
       },
     }
   },

src/commands/force-snip.ts

@@ -1,3 +1,4 @@
+import type { UUID } from 'crypto'
 import { randomUUID } from 'crypto'
 import type { Command, LocalCommandCall } from '../types/command.js'
 import type { Message } from '../types/message.js'
@@ -25,7 +26,7 @@ const call: LocalCommandCall = async (_args, context) => {
   // Collect UUIDs of every message that will be snipped (everything currently
   // in the conversation). The next call to `snipCompactIfNeeded` will honour
   // the boundary and strip these from the model-facing view.
-  const removedUuids = messages.map(m => m.uuid)
+  const removedUuids = messages.map(m => m.uuid).filter((u): u is UUID => !!u)
 
   const boundaryMessage: Message = {
     type: 'system',

src/services/compact/snipCompact.ts

@@ -126,12 +126,15 @@ export function snipCompactIfNeeded(
   }
 
   // Filter out messages whose UUIDs are listed in removedUuids
-  const removedSet = new Set(removedUuids)
+  // Guard: filter out any falsy entries (e.g. messages that lacked a uuid)
+  const removedSet = new Set<string>(
+    removedUuids.filter((u): u is string => typeof u === 'string'),
+  )
   const kept: Message[] = []
   let tokensFreed = 0
 
   for (const msg of messages) {
-    if (removedSet.has(msg.uuid)) {
+    if (msg.uuid && removedSet.has(msg.uuid)) {
       tokensFreed += estimateMessageTokens(msg)
       continue
     }

src/services/compact/snipProjection.ts

@@ -46,7 +46,7 @@ export function projectSnippedView(messages: Message[]): Message[] {
         | undefined
       if (meta?.removedUuids) {
         for (const uuid of meta.removedUuids) {
-          removedSet.add(uuid)
+          if (typeof uuid === 'string') removedSet.add(uuid)
         }
       }
     }

src/utils/sessionStorage.ts

@@ -1996,7 +1996,9 @@ function applySnipRemovals(messages: Map<UUID, TranscriptMessage>): void {
   for (const entry of messages.values()) {
     const removedUuids = (entry as WithSnipMeta).snipMetadata?.removedUuids
     if (!removedUuids) continue
-    for (const uuid of removedUuids) toDelete.add(uuid)
+    for (const uuid of removedUuids) {
+      if (uuid) toDelete.add(uuid)
+    }
   }
   if (toDelete.size === 0) return