fix(input): an oversized paste no longer poisons the durable input queue (#484)

A single input over MAX_INPUT_LENGTH (64 KiB) was queued for reliable
delivery, refused by both transports (the WebSocket silently, POST with a
400), and never dropped: the client treated the 400 as transient, so the
frame was re-sent every 2 s forever, blocked every later input for that
session, and came back from localStorage on every reload.

- Client: a paste over the frame limit is split into in-limit frames
  (never cutting a surrogate pair) delivered in seq order; over 1 MiB, or
  an oversized mux write, it is refused with a toast and never queued.
- Client: the POST drain drops a frame answered 400/413; a WS error ACK
  drops it too; frames over the limit persisted by an older build are
  pruned on load.
- Server: the WebSocket answers an oversized sequenced frame with
  {t:'ia',seq,err:'too_large',max} instead of silence (an older client
  reads that as a plain ACK and drops it); the POST schema uses
  MAX_INPUT_LENGTH instead of a second 100000 limit.

Verified end to end on an isolated instance: a 110 KB paste reached the
PTY byte-identical over both the WebSocket and the POST path, a poisoned
120 KB persisted frame was pruned on load, and a 2 MB paste showed the
refusal toast with nothing queued.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/schemas.ts

@@ -20,6 +20,7 @@ import {
 import { MAX_EDITABLE_BYTES } from '../config/file-editing.js';
 import { MIN_MATCH_LENGTH, MAX_MATCH_LENGTH } from '../config/agent-wait.js';
 import { MAX_WAKE_MACS } from '../config/remote-wake-limits.js';
+import { MAX_INPUT_LENGTH } from '../config/terminal-limits.js';
 import { enabledCliIds, enabledClis } from '../config/cli-registry/registry.js';
 import type { SessionMode } from '../types.js';
 
@@ -1500,7 +1501,10 @@ export const SettingsUpdateSchema = z
  * Schema for POST /api/sessions/:id/input with length limit
  */
 export const SessionInputWithLimitSchema = z.object({
-  input: z.string().max(100000), // 100KB max input
+  // One limit for both transports (issue #484): the route's own length check and
+  // ws-routes.ts read the same constant, so a schema cap above it only hid which
+  // check refused the input.
+  input: z.string().max(MAX_INPUT_LENGTH),
   useMux: z.boolean().optional(),
   // Reliable-delivery dedup (optional; absent for curl/legacy clients). The web
   // client tags each input with a stable clientId + a monotonic per-session seq