slim the submit schemas: evidence and messages die; stringified-payload heal at the pre-validation seam

OpenRouter log diagnosis (owner, 2026-09-28): extraction time was
dominated by tool-validation retries. The failing call had the whole
propositions array emitted as ONE JSON-STRING ('propositions.0: must
be object'), a truncated placeholder artifact inside it, and
word-salad statements late in the array — payload-size collapse.
Field audit: 'evidence' was never persisted anywhere and its
faithfulness-checking consumer died with the fully-trusted ruling;
'messages' fed messageId granularity that NOTHING downstream reads,
and the model sent [] anyway (chat-level provenance in practice).
'aliases' stays (optional now): the auditor's find tool globs them.

Schema: propositions = {id, name, statement, aliases?}; edges =
{from, to, type}. Prompts lose the evidence/messages doctrine and
[id]-anchor guidance, gain a compact faithfulness line;
transcriptView renders anchorless. The auditor echo instruction
drops the evidence/messages mention, so its payload halves too.

Heal: healStringifiedArrays on the submit tool's prepareArguments
(pi-agent-core's sanctioned pre-TypeBox shim) parses a stringified
propositions/edges back into arrays — the LaTeX-restore doctrine:
heal weak-model wire behavior at the seam. Test drives the real
agent-loop seam with a stringified submit.

src/core/session-markdown.ts

@@ -4,9 +4,11 @@
  * The extractor's view of a teaching session and the future user-facing
  * session export share this engine: a session is rendered as clean,
  * readable markdown — speaker headers, quiz/check-in blocks, tool notes —
- * with the message-id anchors preserved (extraction provenance depends on
- * the extractor reporting the `[id]` tags it saw; `anchors: false` mints
- * the same document without them, for the user export).
+ * with optional message-id anchors. Since the submit-schema slim
+ * (2026-09-28) propositions no longer report message ids — the extractor
+ * renders anchorless and provenance is chat-level — so the anchors today
+ * serve only the future user-facing export; `anchors: false` mints the
+ * same document without them.
  *
  * Pure core: native messages in (LhMessage), string out. Content parity
  * with the coverage line builder (core/coverage.ts messageViewLines) is