6e7ca1830e
PRD: add Phase 20 (model matrix, wired) and Phase 21 (context stability, partial). Phase 21 exists because LLM Team hit this exact wall — running multi-model ranking on large context silently truncated, rankings degraded, no pipeline caught it. The stable answer: every agent call goes through a budget check against the model's declared context_window minus safety_margin, with a declared overflow_policy when the check fails. config/models.json: - context_window + context_budget per tier - overflow_policies block: summarize_oldest_tool_results_via_t3, chunk_lessons_via_cosine_topk, two_pass_map_reduce, escalate_to_kimi_k2_1t_or_split_decision - chunking_cache spec (data/_chunk_cache/, corpus-hash keyed) agent.ts: - estimateTokens() chars/4 biased safe ~15% - CONTEXT_WINDOWS table (fallback; prod reads models.json) - assertContextBudget() — throws on overflow with exact numbers, can bypass with bypass_budget:true for callers with their own policy - Wired into generate() and generateCloud() so EVERY call is checked scenario.ts: - T3 lesson archive to data/_playbook_lessons/*.json (the old /vectors/playbook_memory/seed path was silently failing with HTTP 400 because it requires 'fill: Role xN in City, ST' operation shape) - loadPriorLessons() at scenario start — filters by city/state match, date-sorted, takes top-3 - prior_lessons.json archived per-run (honest signal for A/B) - guidanceFor() injects up to 2 prior lessons (≤500 chars each) into the executor's per-event context - Retrospective shows explicit "Prior lessons loaded: N" line Verified: mistral correctly rejects a 150K-char prompt (7532 tokens over), gpt-oss:120b accepts it with 90K headroom. The enforcement is in-band on every call now, not an afterthought. Full chunking service (Rust) remains deferred to the sprint this feeds: crates/aibridge/src/budget.rs + chunk.rs + storaged/chunk_cache.rs