audit(0090): cycle + C24 milestone close — fieldtest green; ledger + rm ephemeral spec/plan

Closes the cycle-0090 (#156) work and delivers the "Topology-as-data:
blueprint serialization & loader (C24)" milestone.

Cycle-0090 audit (architect drift review, range 7ad7f58..HEAD): drift-clean
on substance. Tier-1 forward-tolerance is genuinely serde-default
(deny_unknown_fields = 0 in every production struct), pinned at envelope +
primitive across both the in-crate and public-seam tests; Tier-2 refusals
real and green; no struct/signature/runtime change; the invariant-5
acyclicity lockstep (construction gate <-> bootstrap Kahn sort) undisturbed;
invariant-9 resolver stays injected, no registry. The one medium item the
architect flagged — the C24 Remaining block carried no deferral signal for
#158/#159 — is fixed in this commit's ledger update.

Milestone fieldtest (fieldtests/milestone-topology-as-data/, the close-gate
evidence): GREEN, 0 behavioural bugs. A downstream consumer ran the full
author -> serialize -> load -> construct -> introspect -> reproduce story from
the public surface alone — round-trip bit-exact on both authoring surfaces
(Rust builder + op-script CLI), build-free introspection, Tier-1/Tier-2
forward-compat by name, fail-fast diagnostics by identifier. Verified the
headline claims myself (the two Rust binaries + the CLI build/diff + the
fail-fast exits), not just the agent's report.

Findings triaged to the forward queue (none blocking): op-script grammar
undocumented + a stale cycle-0088 example (#163); canonical trailing-newline
divergence + Composite Debug/PartialEq ergonomics (#164); CLI discoverability
of build/introspect + no `graph run` (commented on #159); the newline as a
content-addressing prerequisite (commented on #158).

#158 (content-address topology in the manifest) and #159 (retire the
hard-wired harnesses) were moved OUT of this milestone: both are premature
until the World generates runs from blueprint-data (commit still fully
identifies every hard-wired topology), so they belong to the
project-as-crate / World cycle. The C24 ledger Status records the delivery
and the deferral.

Ephemeral cycle-0090 spec + plan removed per the lifecycle convention.
The Gitea milestone container is closed on user ratification (this run
tees up the close, does not click it).

docs/design/INDEX.md

@@ -1829,9 +1829,8 @@ node type, edge semantics, or structural-axis kind) bumps `format_version` so an
 old reader refuses cleanly (`LoadError::UnsupportedVersion` / `UnknownNodeType`,
 already green). The per-section required-flag scheme is deferred (no current
 Tier-2 section to validate it; recorded on #156).
-**Remaining**
-(each its own milestone issue):
-content-addressed topology identity in the manifest (#158, C18); retiring the pre-C24
+**Milestone delivered — 2026-06-30, cycle 0090 — the serializable format + loader + construction service.** A green end-to-end milestone fieldtest (`fieldtests/milestone-topology-as-data/`) proves the full author → serialize → load → construct → introspect → reproduce story from the public surface alone, 0 behavioural bugs; the round-trippable format (#155), the construction service (#157), and the forward-compat two-tier discipline (#156) all shipped. Polish filed forward: op-script grammar docs + a stale example (#163), the canonical trailing-newline / `Composite` value ergonomics (#164), CLI discoverability of `build`/`introspect` (#159).
+**Deferred to the World / project-as-crate cycle** (moved out of this milestone — they address a problem that only arises once the World *generates* runs from blueprint-data, which does not exist yet: `commit` still fully identifies every hard-wired topology): content-addressed topology identity in the manifest (#158, C18) — premature until a run is built *from* a serializable blueprint; retiring the pre-C24
 hard-wired `aura-cli` harnesses (`HarnessKind`, `run_stage1_r`, `*_sweep_family`) once
 the project-as-crate layer lands (#159, paired with #157's data-authoring surface). **Out of the first cut's round-trippable set**
 (deliberate; fails clean as `UnknownNodeType`, never a silent wrong graph): recording