practice hardening: weak-model argument heal + parked dismissals mid-turn

The GLM incident (2026-10-04): glm-5.3 sent mode as a JSON-string-encoded
enum ('"recall"') on 19 consecutive problem calls; TypeBox's error never
named the expected values, so the model re-emitted the identical payload
until the dev server was killed. And mid-turn the learner was trapped:
Esc's question/problem rungs only dismissed — the dismiss route 409'd
against the turn-owned record and nothing could stop the running turn.

- healEncodedArguments (practice.ts, the prepareArguments seam): a STRING
  where the schema expects a literal union / boolean / null / number /
  array is JSON.parse-d and kept when it satisfies the schema. Valid args
  pass through untouched (same reference); unhealable values stay for
  validation to reject honestly. Wired on BOTH problem and conclude.
- dismissal-park.ts: the dismiss route parks a mid-turn dismissal (202);
  the turn's settle path (onFinish, after persistTurn, before endTurn —
  the same ordering law as the record write itself) applies it against
  the persisted record, only if the dismissed thing really is pending.
- confirmAbort: question/problem discard while busy now ALSO aborts the
  in-flight turn; the dialog line says so (busy prop).

No error-result cap (owner ruling). 16 new pins (heal incl. pi-ai
validateToolArguments end-to-end; park registry, apply paths, the 202
route contract).

src/server/chat-handler.ts

@@ -35,6 +35,7 @@ import {
 } from "../core/settings-resolution.ts";
 import { modelsNotConfigured, providerKeyMissing as providerKeyMissingEnvelope, type ProviderKeyMissing } from "../core/settings.ts";
 import { beginTurn, endTurn } from "./turn-liveness.ts";
+import { applyParkedDismissal } from "./dismissal-park.ts";
 import { registerTurn, unregisterTurn } from "./turn-runs.ts";
 import { persistTurn, triggerExtraction } from "./turn-service.ts";
 import { hasProbeDone, danglingQuestionOf } from "../core/native-messages.ts";
@@ -426,6 +427,13 @@ export async function handleChatInput(
 					// against it and the pipeline's batches share it.
 					triggerExtraction(stores, extraction, chatId, effective.graph.extractionChunkTokens);
 				}
+				// PARKED DISMISSAL (owner, 2026-10-04): a dismissal that arrived
+				// mid-turn was parked by the dismiss route (202); now that
+				// persistTurn has landed the turn's messages, apply it against
+				// real truth — BEFORE endTurn, so "turn-settled" guarantees a
+				// subsequent fetch reads the dismissal already in the record
+				// (the same ordering law as persistTurn itself).
+				applyParkedDismissal(stores.chatStore, chatId);
 				// LAST: a poller that sees not-in-flight must read an already-persisted
 				// record — endTurn only after persistTurn has done its job.
 				endTurn(chatId);