docs(#3467): adr-3408 state.md write-path behavior contract (#3474)

* docs(#3467): adr-3408 state.md write-path behavior contract

* docs(#3467): correct write-seam caller list and adr heading depth

Review findings from the Standards and Spec axes, fixed in place:

- ADR behavior contract demoted from H2 to `### 8` with `#### 8.x`
  subsections, matching ADR-3180's `### 7` / `#### 7.1` precedent the
  front matter claims to follow.
- CONTEXT.md placed the STATE.md factory-reset primitive at
  verify.cts:1925. It moved to health-diagnostic.cts:337 when
  cmdValidateHealth migrated onto the rule table (#3309); verify.cts
  now has no writeStateMd call. The design intent was correct — only
  the address was stale.
- A repo-wide scan found three direct writeStateMd callers, not two:
  cmdStateSync, cmdMilestoneComplete, and the REGENERATE_STATE remedy.
  The last is documented as a sanctioned permanent exception — it is
  a factory reset, so preservation would restore the values it was
  invoked to discard.
- phase.cts comment citation corrected to :2953-2957.
- Amendment 4 attribution corrected: the recorded owner-file exemption
  failure is roadmap-parser.cts; the state.cts transfer is this ADR's
  own extrapolation.

---------

Co-authored-by: sim <sim@local>

docs/adr/README.md

@@ -252,6 +252,7 @@ These govern the system as it stands. Cite these.
 | [ADR-2980](2980-payload-carried-error-is-a-degraded-result.md) | A payload-carried `error` key is a degraded result, not a fault | Accepted | — |
 | [ADR-3180](3180-planning-semantic-model-single-owner.md) | Planning Semantic Model — Single Owner per Derivation | Accepted | — |
 | [ADR-3212](3212-lexical-seam-consolidation.md) | The Lexical Seam — Safe Pattern Construction, Line-Terminator Normalization, and Tokenizer-First Stateful Grammars | Accepted | — |
+| [ADR-3408](3408-state-write-path-preservation.md) | STATE.md Write Path — One Declared Policy, One Write Seam | Accepted | — |
 | [ADR-3660](3660-runtime-artifact-layout-module.md) | Runtime Artifact Layout Module owns per-runtime artifact placement | Accepted | [ADR-1239](1239-gsd-embeddable-orchestration-engine.md) |
 
 ### Proposed