feat(#2101): dogfood ZCode through the EoS declarative adapter + fold shared-hooks exclusion (ADR-1239)

The issue's "0 conditional branches" premise missed a live one: the `!isZcode`
shared-hooks exclusion (bin/install.js). Fold it onto descriptor-driven
hostBehaviors.skipSharedHooksInstall:true (zcode's golden has zero hook files —
byte-parity verified) and drop the now-unused isZcode destructure. Zero live
runtime==='zcode'/isZcode branches remain (AC2 source-grep guard over
bin/install.js + install-engine.cts + surface.cts + runtime-artifact-conversion.cts).
The 6 CLI-bookkeeping zcode mentions (--zcode flag, menu, roster, help) stay.

Reference test (declarative-reference-zcode.test.cjs): profileOf → declarative-cli;
createDeclarativeAdapter({runtime:'zcode'}).kind → declarative; a real install emits
the invocable nested-skills/commands/agents surface (no hooks); negotiateHostCapabilities
fail-closes (empty/corrupt descriptor; the nested/maxDepth undocumented sub-axes degrade
to most-restrictive); validateCapability clean.

UPGRADES documented as BLOCKED (verified doc gaps — NOT guessed, to avoid a
non-functional false-green): both of ZCode's documented capabilities lack a published
on-disk config format.
- Hook automation: zcode.z.ai/en/docs/plugin documents the Hook component only as
  "automation hooks triggered on specific events" (capability detected from directory
  layout) — no config file format/location/event schema. Cannot faithfully wire.
- MCP registration: zcode.z.ai/en/docs/mcp-services says servers are "stored in the
  .zcode configuration file" (UI-only) with no documented on-disk filename/path/schema —
  exactly the settings-filename gap the issue AC anticipated.
Both are documented (with the search trail) in the capability matrix + how-to, per AC4's
block-documentation clause; hookBus/transport stay declared for when ZCode publishes the
formats. No hook scripts or MCP artifacts added → no golden change, no other-runtime impact.

Golden: byte-identical for all 16 runtimes (the fold is byte-parity; no upgrade artifacts).
Matrix ## zcode EoS note + how-to; changeset (Changed). capability-registry regenerated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bin/install.js

@@ -8859,7 +8859,8 @@ function install(isGlobal, runtime = DEFAULT_RUNTIME, options = {}) {
   // hostBehaviors.skipSharedHooksInstall respectively; its legacy-agent-loop
   // converter arm was likewise unreachable dead code (windsurf is in
   // _DESCRIPTOR_AGENTS_RUNTIMES) and was removed above.
-  const { isOpencode, isZcode, isCodex, isCursor, isAugment, isTrae, isQwen, isHermes, isCline } = runtimeFlags(runtime);
+  // #2101: isZcode dropped — folded onto hostBehaviors.skipSharedHooksInstall.
+  const { isOpencode, isCodex, isCursor, isAugment, isTrae, isQwen, isHermes, isCline } = runtimeFlags(runtime);
   const plan = resolveInstallPlan(runtime);
   const dirName = getDirName(runtime);
   const src = path.join(__dirname, '..');
@@ -10026,7 +10027,8 @@ function install(isGlobal, runtime = DEFAULT_RUNTIME, options = {}) {
   // skipSharedHooksInstall:true) — the redundant `&& !isKilo` was removed.
   // #2094: Trae's exclusion is likewise descriptor-driven (trae declares
   // skipSharedHooksInstall:true) — the redundant `&& !isTrae` was removed.
-  // ZCode still has an empty hostBehaviors, so `&& !isZcode` stays.
+  // #2101: ZCode's exclusion is likewise descriptor-driven (zcode declares
+  // skipSharedHooksInstall:true) — the redundant `&& !isZcode` was removed.
   // #2095: Kimi's exclusion is likewise descriptor-driven (kimi declares
   // skipSharedHooksInstall:true) — kimi's shared hooks/ + package.json marker
   // are instead installed into its OWN native hook root (~/.kimi, resolved by
@@ -10037,7 +10039,7 @@ function install(isGlobal, runtime = DEFAULT_RUNTIME, options = {}) {
   // skipSharedHooksInstall:true) — the redundant `&& !isCopilot` was removed.
   // #2100: Windsurf's exclusion is likewise descriptor-driven (windsurf declares
   // skipSharedHooksInstall:true) — the redundant `&& !isWindsurf` was removed.
-  if (!isCodex && _hostBehaviors(runtime).skipSharedHooksInstall !== true && !isZcode) {
+  if (!isCodex && _hostBehaviors(runtime).skipSharedHooksInstall !== true) {
     if (!installSharedHooksBundle(targetDir)) {
       failures.push('hooks');
     }