fix(copilot): match a size refusal by its whole shape, not its prefix

isOversizedReadPlaceholder tested startsWith, so a real one-line file opening
with one of those prefixes was returned to the model as a tool error instead of
its contents. Every builder emits the same '(N bytes, limit M)]' tail, so
requiring the full shape costs nothing and makes an accidental collision
implausible. The pattern is built from the same prefix table, so it cannot drift
from the producers.

Author: waleedlatif1

apps/sim/lib/copilot/tools/handlers/vfs.test.ts

@@ -205,6 +205,23 @@ describe('vfs handlers oversize policy', () => {
     expect(result.error).toBe(content)
   })
 
+  it('returns a real file that merely opens like a size refusal', async () => {
+    // Prefix-only matching would turn this user's file into a tool error. The
+    // refusal is recognised by its whole shape, which real prose does not have.
+    const vfs = makeVfs()
+    const content = '[Document too large to parse inline: is the message we emit here]'
+    vfs.readFileContent.mockResolvedValue({ content, totalLines: 1 })
+    getOrMaterializeVFS.mockResolvedValue(vfs)
+
+    const result = await executeVfsRead(
+      { path: 'files/notes.md/content' },
+      { userId: 'user-1', workflowId: 'wf-1', workspaceId: 'ws-1' }
+    )
+
+    expect(result.success).toBe(true)
+    expect((result.output as { content?: string })?.content).toBe(content)
+  })
+
   it('returns an undecodable image placeholder as content, not as a size failure', async () => {
     const vfs = makeVfs()
     // Not a size problem — the bytes were read fine and the reason is already in the

apps/sim/lib/copilot/vfs/read-placeholders.ts

@@ -57,8 +57,23 @@ const OVERSIZED_PREFIXES = [
 /** Every placeholder — none of them carry text worth searching. */
 const NON_GREPPABLE_PREFIXES = Object.values(PREFIX)
 
+function escapeRegex(literal: string): string {
+  return literal.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+}
+
+/**
+ * Matches a size refusal in full rather than by prefix. Every builder above emits the
+ * same `… (N bytes, limit M)]` tail, so requiring it costs nothing and stops a real
+ * one-line file that merely opens with this text from being turned into a tool error
+ * instead of being returned. Built from {@link OVERSIZED_PREFIXES} so it cannot drift
+ * from the producers. One unnested `.+` against a fixed suffix — no backtracking.
+ */
+const OVERSIZED_PATTERN = new RegExp(
+  `^(?:${OVERSIZED_PREFIXES.map(escapeRegex).join('|')}) .+ \\(\\d+ bytes, limit \\d+\\)\\]$`
+)
+
 export function isOversizedReadPlaceholder(content: string): boolean {
-  return OVERSIZED_PREFIXES.some((prefix) => content.startsWith(prefix))
+  return OVERSIZED_PATTERN.test(content)
 }
 
 /**