docs: unify ADR/RFC trees into one lifecycle-organized RFC tree

Collapse docs/adr/ and docs/rfc/ into a single docs/rfc/ with proposed/,
implemented/, and rejected/ subfolders. Every file is renamed to
yyyy-mm-dd-topic-title.md, where the date is when the topic was first
proposed (from git history). ADRs and RFCs that covered exactly the same
topic are merged (property-based testing, session persistence); the
umbrella RFC 005 stays split across its three implemented decisions, and
RFC 006's deferred part-3 (API extractor reports) splits into its own
proposed RFC. All cross-references become machine-checkable relative
links instead of bare "ADR NNNN" / "RFC NNN" prose.

Add a verify-md-links doc-sync gate (scripts/verify-md-links.ts) that
checks every relative Markdown cross-link resolves, wired into doc-sync
alongside verify-md-wrap. This makes the reorganization self-verifying:
the same change that rewrote ~forty inter-doc links adds the check that
proves none dangle. Document the cross-link convention in a new
docs/AGENTS.md and record the gate as an implemented RFC.

doc-sync, typecheck, lint, and the full test suite (667) all pass.

packages/tools/tests/properties.spec.ts

@@ -1,8 +1,8 @@
 /**
- * Property-based tests for the tool-schema DSL (RFC 001 → ADR 0013), including
- * the RFC 001 ↔ 005 composition: generated args that satisfy a SchemaSpec must
+ * Property-based tests for the tool-schema DSL (the property-testing RFC), including
+ * the the property-testing ↔ runtime-validation composition composition: generated args that satisfy a SchemaSpec must
  * pass validateArgs, and targeted corruptions must be rejected. This closes the
- * validator/InferArgs drift risk noted in ADR 0011.
+ * validator/InferArgs drift risk noted in the arg-validation RFC.
  */
 
 import { describe, expect, it } from 'vitest'
@@ -108,7 +108,7 @@ describe('schema DSL properties', () => {
     }))
   })
 
-  it('RFC 001↔005: args satisfying the spec pass validateArgs', () => {
+  it('the property-testing ↔ runtime-validation composition: args satisfying the spec pass validateArgs', () => {
     fc.assert(fc.property(
       specArb(2).chain(spec => fc.tuple(fc.constant(spec), validArgsForSpec(spec))),
       ([spec, args]) => {
@@ -117,7 +117,7 @@ describe('schema DSL properties', () => {
     ))
   })
 
-  it('RFC 001↔005: dropping a required key is always rejected', () => {
+  it('the property-testing ↔ runtime-validation composition: dropping a required key is always rejected', () => {
     fc.assert(fc.property(
       specArb(1)
         .filter(spec => requiredKeys(spec).length > 0)
@@ -132,7 +132,7 @@ describe('schema DSL properties', () => {
     ))
   })
 
-  it('RFC 001↔005: a non-object top level is always rejected', () => {
+  it('the property-testing ↔ runtime-validation composition: a non-object top level is always rejected', () => {
     fc.assert(fc.property(
       specArb(1),
       fc.oneof(fc.string(), fc.integer(), fc.boolean(), fc.constant(null), fc.array(fc.anything())),

packages/tools/tests/tools.spec.ts

@@ -609,7 +609,7 @@ describe('ToolRegistry.get', () => {
   })
 })
 
-describe('validateArgs (RFC 005 part 1)', () => {
+describe('validateArgs (the runtime-validation RFC, part 1)', () => {
   it('returns [] for valid args and is total over malformed input', () => {
     const spec = {
       path: { type: 'string', required: true },
@@ -709,7 +709,7 @@ describe('validateArgs (RFC 005 part 1)', () => {
   })
 })
 
-describe('defineTool validation (RFC 005 part 1)', () => {
+describe('defineTool validation (the runtime-validation RFC, part 1)', () => {
   it('returns an isError result with the violations when the model sends bad args', async () => {
     const ctx = await setup()
     ctx.tools.register(defineTool({