fix: the handoff freeze + the free-form mermaid pass

Two user-reported problems from the muscle-protein-synthesis session,
both diagnosed from the live data (chat_mtxeml9e_6118e59f).

The freeze: after probe_done, the open session never showed the
teacher's wake turn — only navigating away and back loaded it. Not an
agent-switch problem: the server-side handoff worked perfectly
(write-ahead persist, liveness registry, the sidebar's busy dot saw the
wake the whole time). The gap was client attach: the only mid-session
wake detector the open page has is the jobs poll, and probe-phase
sessions have zero job traffic, so that poll is OFF; the post-turn
adoption poll read turnInFlight=false at ~0ms (the wake fires at
~0.75-1.2s, after the pump's grace), adopted, and stopped. Fix: the
post-turn adoption effect now keeps a short WATCH WINDOW after adopting
(~4s, 8x500ms) — if turnInFlight flips true, it hands off to the
existing wake-adoption poll (busy shimmer, adopt at finish).

The mermaid failures: four failed plan_init calls, all caused by ONE
hidden rule — underscores are forbidden in node ids (mps_translation,
net_balance, per_meal). The id regex rejected '_' BEFORE the slug check,
so the specific, actionable message never fired; the generic 'can't read
the edge — expected a[title] --> b[title]' lied (the syntax was exactly
that), and the teacher spent three attempts hunting punctuation it
suspected (colons, commas, multi-word labels) — visible in its own
reasoning trail. Per the user's principle — enforce only the slugs,
free everything else: underscores are first-class slug chars; the id
CANDIDATE class is broad so every bad id reaches the specific slug
message; chained edges (a --> b --> c) expand to pairs; ==>, -.-> are
edge synonyms; any direction header accepted (we layout ourselves);
id["title"] quote pairs are stripped. The tool description, zod
describe, and the teacher's planning prompt now state the one strict
rule instead of the old subset liturgy.

Verified: tsc, 305/305 (the exact muscle-protein mermaid is now a
passing test), lint, build; real-browser puppeteer smoke on live GLM —
the teacher's wake turn appeared in the open page ~50s after the probe
concluded with ZERO navigation, verdict gate + first teach check +
plan window all live in-page (the single console 404 is the app's
missing favicon, environmental noise).

src/agent/prompts/teacher/10-planning.md

@@ -27,7 +27,7 @@ Mermaid stays for ad-hoc lesson diagrams — the plan map is a different thing a
 The map is a **map, not a syllabus**.
 
 - One reasoning step per node. If a node needs three explanations to teach, it's three nodes.
-- Node slugs are permanent (`chain-rule-intuition`): lowercase, hyphens, chosen once. Labels ≤ 6 words.
+- Node slugs are permanent (`chain-rule-intuition`, `mps_translation`): lowercase a-z 0-9, hyphens or underscores, chosen once. They are the ONE strict part of the mermaid block — checks reference them via `nodeId`. Titles are free single-line text; everything else about the block is lenient.
 - Typically 5–15 nodes per session. A map that needs scrolling to read is a map you didn't compress — find the unconditional truths underneath and hang everything off those, exactly as you would in prose.
 - `-->` edges are `requires` edges: from = must be understood before to. Direction is a teaching fact, not decoration.