fix(splice): derive recent-problems from problem-card frontmatter — the KNOWLEDGE.md zombie lies to every session (#654)

[aarontrowbridge]

Closes #654

What

Every session's system prompt derived "Your recent problems" from KNOWLEDGE.md — a vault index file frozen by design (the distiller stopped writing it) whose lines had gone stale: it claimed a problem was "solved 20×" while the problem card it links records 29 solves. The distillate's actual source of truth — the problem cards' frontmatter, maintained, versioned, provenance-clean — was one indirection away and unread.

The splice now derives the section directly from problem-card frontmatter: scan <vault>/amicode/problems/*.md, parse frontmatter (slug, platform, kind, target, status, best fidelity, solve count, last-seen), sort by last-seen freshest-first, cap at the same 50-line budget, render the same section format the prompt already consumes. The zombie index is dead; every future session sees the truth.

Acceptance criteria — evidence

• Derived from frontmatter, not KNOWLEDGE.md — sort/order/cap/malformed-skip covered by new tests (22/22 in the splice suite): cards sort by last_seen freshest-first, 60 cards cap to 50 bullets, malformed frontmatter skips, missing last_seen sorts last, zero cards omits the section.
• Format-compatible with the current prompt — a golden test pins the full rendered block byte-for-byte against the distiller spec's documented historical line shape, warm-start guidance footer included.
• The zombie lie is dead — the named test: a card recording 29 solves is reported even when the frozen index still claims 20 (toContain('solved 29×'), not.toContain('20×')). Verified end-to-end against the live vault: 23 cards, x-gate reports solved 29×, best F verbatim 0.9999858416888963 (the splice never re-rounds a fidelity — the old index's rounded 0.999986 was itself a small lie).
• No product code reads KNOWLEDGE.md — grep clean: only the test's deliberate stale fixture and doc comments remain. (The distiller agent's prompt-level match-before-create read of the file is documented behavior, out of this slice's scope; DEMOS.md's frozen-but-read status is a separate flagged slice.)

Director gates (run independently on this branch)

• pnpm --filter amicode typecheck — clean
• Full extension suite env-scrubbed — 1752 passed / 3 failed, and the 3 failures verified pre-existing on pristine origin/main (pasqal venv sandbox + the terminal env-injection family, known issue test: agent-spawn env test is non-hermetic — fails under OPENCODE_CONFIG_CONTENT (server sessions) #645 class) — zero regressions
• stack_state.test.ts — 22/22
• Live-vault end-to-end: 23 cards scanned, truth rendered
• Process note: the branch was originally cut at ea169ec; origin/main advanced past it mid-slice (feat: amicode_session tool — spawn sessions from a session as background tabs #639/skill: open-threads — sweep recent sessions, propose a consolidated spawn plan #646/feat(hub-ops): Amicode: Restart Hub Server — client-initiated atomic hub restart #649-650 merged), so the branch was rebased onto current main before final gating — the rebase was clean (no conflicts; splice files untouched by the new merges).

Design choices worth review

• Hand-rolled frontmatter parser rather than reusing the repo's YAML parser: stack_state.ts is pinned node-builtin-only (the plugin's embedded runtime can't resolve the extension's deps — the same reason its TOML marker parsing is regex-lite). The parser is defensive: malformed cards are skipped, never crash the splice.
• Fidelities render verbatim from the card — no re-rounding (toFixed(6) would round 0.9999997 up to 1.000000).
• attempted/failed problems render "ATTEMPTED (N failed)" from solve_count, dropping the old wording that conflated failed runs with solve count.
• pulse_ref's pulses/ prefix is stripped to preserve the historical pulse: <id> line shape.

Leftovers flagged (not this slice)

• DEMOS.md is also frozen-but-spliced — same disease, separate slice.
• The distiller agent's prompt-level read of KNOWLEDGE.md (match-before-create) is documented behavior, not a code path — revisit when the distiller transport is re-armed.

Merge

Awaiting human review per the campaign's standing discipline. CI runs on this PR.

[coderabbitai]

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