test(xce-harness-component): verify build isolation; narrow requirement 2.2

Validation task 4.3 found a real, deterministic conflict with the
original requirement 2.2 wording, not a flake: /xce-build controller
alone's default asan profile transitively rebuilds harness/xce_test,
because Meson's test-runner rebuilds every registered test's build-
order dependencies project-wide before filtering by --suite, and
harness_unit_test (task 2.1) depends on it. Confirmed via build-log
step-count analysis (explicit compile: 209 steps, clean; subsequent
meson test: 844 steps, resurrects it) and independently reproduced
twice, with an exact step-count match both times.

User decision (2026-09-14): accept as a documented Meson limitation
rather than auditing every component's test-target list (controller's
own suite already relies on this same mechanism for 4 of its own test
binaries) or weakening harness_unit_test's build-order guarantee
(verified load-bearing in task 4.2). Requirement 2.2 narrowed to what
the build system directly controls: its explicit compile-target list
never names xce_test. requirements.md/design.md/tasks.md updated to
match and cross-reference each other; logged as bug-1806 (accepted,
not fixed) for the record.

Also commits the xce-harness-component spec's remaining docs
(requirements.md, brief.md, research.md, spec.json) and the roadmap.md
promotion entry from discovery, none of which had been committed yet.

Task 4.3 of xce-harness-component.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLSNJhNoULvVcUhXEFafQC

.kiro/steering/roadmap.md

@@ -62,6 +62,7 @@ The protocol **drive** is NOT fully event-driven. Root cause: `peer_ctrl_msg_han
 
 ## Future Specs / Backlog (dependency order)
 
+- [ ] **xce-harness-component** — **PROMOTED to spec 2026-09-13** (`/kiro-discovery`; brief at `.kiro/specs/xce-harness-component/brief.md`). Elevate `xce_test` (the REPL-driven wire-protocol test client used by HA soak / multi-host / resource-value verification) out of `src/controller/testsuite/` into its own first-class `src/harness/` component — own `meson.build`, `CLAUDE.md`, and unit-test binary (carved out of `controller_unit_test`, which today recompiles ~14 of xce_test's own files a second time paired with white-box tests) — fully decoupled from `/xce-build controller` (today's implicit "controller always builds xce_test" coupling, `build-deployment.md:24`). Verified finding: none of xce_test's 15 source files include any controller-private header — only libxce public headers + generated capnp schema — so this is a pure relocation + build-graph split, not a dependency untangling problem, and no xce_test behavior changes. Touches `/xce-test-ha`, `/xce-deploy-ha`, `/xce-test-multihost`, `/xce-test-resources` (each must build `harness` explicitly once decoupled) and is adjacent to (not overlapping) the three existing behavior specs `xce-test-cli-ux`/`xce-test-e2e-primitives`/`xce-test-rc-file`, whose file-path references go stale after the move. Next: `/kiro-spec-init xce-harness-component`.
 - [ ] config-upgrade-snapshot — **descoped from `ha-term-safety` R8 on 2026-06-21 (requirements generated; `.kiro/specs/config-upgrade-snapshot/`).** Closes **bug-857**: a configuration upgrade can leave members with DIVERGENT materialized state because today it does config-push + restart + per-node WAL replay under the new config (`config_repl.c` `do_upgrade_config_with_bytes` ~1001-1163), with no snapshot pinning an identical post-upgrade state (replay is config-dependent — `lost_and_found` re-homes orphaned entities). Approach: an upgrade materializes a **full entity-bearing state snapshot at the config-change marker's `(term,lsn)` boundary**, embeds the new config, and installs it on every member via the `snapshot_transfer_s` transport — no per-node re-derivation; supersedes `ha-term-safety` R7's interim config-push byte delivery for upgrades. **Former HARD dependency `entity-bearing-snapshots` is CLEARED** — it shipped as spec `ha-entity-snapshots` (**IMPLEMENTATION-COMPLETE, validate-impl GO 2026-07-18**; see Future Specs/Backlog below), and `ha-term-safety` (the config-change marker it anchors on) is also implemented. `config-upgrade-snapshot`'s own `spec.json` now has `blocked_on: []`. Verify by reproducing bug-857 (upgrade during chaotic multi-kill, diff materialized state). **Ready to promote to design.**
 - [ ] component-failover-adoption — **recorded 2026-06-16; depends on libxce-failover (HARD).** Make the C daemons and the Go apiserver actually exercise libxce's transparent failover. The mechanism reaches them for free (worker/scheduler/controller link `libxce_dep`; apiserver uses it via cgo, `src/frontend/apiserver/backend/clib.go`), but two per-component integration items remain: (1) each component must hand libxce the **full master list** instead of a single endpoint (today even the CLI uses only `conf->masters[0]`, `client.c:122`); (2) bounded retry makes the already-blocking `xce_request` block **longer** (seconds of backoff) — for the async C daemons (worker `controller_connector.c`, scheduler `handler.c`) this must be verified **liveness-safe**, i.e. it must not stall a thread that also drives heartbeats (the "never block the iomgr thread" rule). Scope: per-component master-list config + retry policy + liveness-safe blocking + per-component E2E failover for **scheduler, worker, apiserver**. (`xce_test` is NOT here — it is the in-spec verification client of libxce-failover.) Promote via `/kiro-spec-init component-failover-adoption` after libxce-failover lands.
 - [x] ~~worker-rejoin-resync~~ — **PROMOTED to spec 2026-08-10, see In Flight (Raft Apply-Ordering family) above** for current status and brief. No longer tracked here.