Backfill architecture decision records

Seven ADRs capturing the why behind decisions already made: vendoring
Cordis as source with a guarded manifest; the microkernel event
taxonomy with one swappable concrete loop; event-sourced sessions
with derived history and the append-before-emit ordering contract;
the provider-neutral content-block vocabulary (and why not
OpenAI/Anthropic shapes); the custom tool-schema DSL over schemastery;
tool schemas living in the prompt assembly; and mechanical quality
gates over prose guidelines (the agents-write-the-code rationale).

docs/adr/0007-quality-gates.md

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+# ADR 0007: Mechanical quality gates over prose guidelines
+
+Status: accepted (2026-06-11)
+
+## Context
+
+This codebase is developed primarily by coding agents. Agents follow enforced
+gates far more reliably than prose conventions, and "a lot of work" is not a
+cost argument when agents do the labor. Early evidence: tests that didn't
+typecheck shipped (vitest doesn't typecheck) and were only caught by a review.
+
+## Decision
+
+Every AGENTS.md promise gets a command that exits non-zero, wired into git
+hooks and CI both calling the same package.json scripts:
+
+- Max-strict TypeScript (`noUncheckedIndexedAccess`,
+  `exactOptionalPropertyTypes`, …); tests and examples typecheck in CI via
+  `tsconfig.typecheck.json` (vendored packages resolve as built declarations).
+- ESLint strict-type-checked + @stylistic (the house style, enforced);
+  vendored code excluded.
+- Per-file 100% coverage on `packages/*/src` (v8); unreachable defensive
+  guards carry `/* v8 ignore */ ` with stated reasons instead of deletion.
+- knip (dead code/deps), publint (package correctness), yarn constraints
+  (workspace rules: private, cordis peer+dev, uniform version, ESM).
+- lefthook pre-commit (lint staged, typecheck, vendor-manifest guard) and
+  pre-push (tests, hygiene); CI runs the full matrix on node 24/26 plus a
+  demo smoke test driving the echo-agent end to end.
+
+## Consequences
+
+- Conventions survive agent turnover; violations fail fast and locally.
+- The gates themselves are code to maintain; config changes are reviewed like
+  any change.
+- 100%-coverage pressure can produce assertion-free tests — mutation testing
+  is the planned counterweight (see RFC 002).