docs(router): reframe matching review as a durable reference - #547

What

Reframes the matching/lazy-discovery internal doc from a point-in-time v1 stability review into a durable architecture & accepted-tradeoffs reference, and renames it to match:

docs/internal/matching-stability-review.md → docs/internal/matching-and-lazy-discovery.md

Docs + code-comments only — no behavior change. Committed with [skip ci].

Why

The review framing had served its purpose: the v1 matching-stability work is done (#535, #537–#541, #544–#546). What was left was ~60% transient process scaffolding — "Pass 1/2 landed" changelog, implementation plan, next actions, the per-finding M/C/R status catalogs, and write-ups of the multi-agent workflows we ran. That half is already captured by git history and the merged PRs, so as a current-state doc it would only rot. The remaining ~40% is genuinely durable and worth keeping as reference.

What the reference keeps

• How matching works — trie canonical, regex latent; the single shared buildPerRouterTrie for both dev and prod.
• The dev/prod contract table — updated to reflect the now-unified builder (no more inline visitPrefixNode row).
• Invariants & design decisions with rationale — the still-relevant findings folded in as decisions rather than changelog: trie precedence (M4), bare-prefix wildcard (C1), joinPrefix normalization (C5), find-match cache clone (C7), shared-staticPrefix omission (C19), leaf-vs-non-leaf precompute (C8), trailing-slash modes (M3).
• Accepted performance tradeoffs — LP1/LP3/LP4 with the measured numbers + the vitest bench lazy-include-cost artifact, framed as "do not re-litigate without re-running the bench."
• Tests that pin each invariant, and a short optional / not-v1 list.

Mechanics

• git mv (history preserved; the large rewrite means git shows it as add+delete in the diff, but --follow tracks it).
• Finding IDs (C1/C5/C19/M3/M4/LP1/LP3/LP4) kept as decision labels so the 5 code-comment cross-references still resolve.
• Updated all 6 references: docs/README.md (nav entry reworded) + 5 code comments (manifest.ts, lazy-includes.ts, trie-regex-parity.test.ts, lazy-include-perf.test.ts, lazy-include-cost.bench.ts). Verified no stale references to the old filename remain.

Test plan

• typecheck / unit 3383 / lint / format clean; pre-commit (lint/format/e2e-bucketing) green
• no behavior change → [skip ci]
• grep confirms zero remaining references to the old filename