feat(#2098): drive CodeBuddy through the EoS descriptor + wire subagent hooks (ADR-1239)

Fold CodeBuddy's residual runtime-literal branches onto descriptor-driven
hostBehaviors (the issue's "zero branches remain" premise was inaccurate — 2
lived):
- Folded the `if (isCodebuddy)` commands/ report duplicate (byte-identical to
  the generic reportCommandsDir block above it) onto
  hostBehaviors.reportCommandsDir:true, matching cursor's #2089 precedent.
- Deleted the dead `else if (isCodebuddy)` agent-conversion arm (codebuddy ∈
  _DESCRIPTOR_AGENTS_RUNTIMES → gated out before the legacy chain, same dead-arm
  pattern removed for augment/trae in #2097).
- Removed isCodebuddy from all 4 destructure sites (now comments only, mirroring
  the #2096 isAntigravity fold). Zero live isCodebuddy reads remain.

UPGRADE 1 (extended hook bus): populate extendedHookEvents with the full
extended set SubagentStop/Stop/PreCompact/SubagentStart (qwen #2092 / kimi
precedent — codebuddy previously had extendedHookEvents:[] so it got NONE of
these). The generic applySettingsJsonHooks loop wires them, so CodeBuddy's
settings.json now gains all four subagent-lifecycle + stop/compact hooks it
previously lacked, matching Qwen/Kimi coverage. No source change (the
HOOK_EVENT_SURFACES SDK catalog is a locked dict; all 4 events are already in
the validator enum; hookEvents already 'claude'). settings.json is golden-
excluded → no golden change.

UPGRADE 2 (background dispatch): surfaced via the negotiated capability contract
only. CodeBuddy's dispatch.background:true legitimately exceeds the declarative-
cli baseline (false) and survives negotiation with no warning. NO agent-file
frontmatter field is emitted: the CodeBuddy CLI (GSD's install target,
~/.codebuddy/agents/) has NO background-dispatch frontmatter field — background
is a caller-side run_in_background invocation param (verified against
codebuddy.ai/docs/cli/sub-agents); the issue's agentMode/enabledAutoRun are
IDE-only (codebuddy.cn, a different product). Emitting them would be a non-
functional false-green, so it is deliberately not done.

Golden: byte-identical for all 16 runtimes (folds are console/failures-report
only; UPGRADE 1 → golden-excluded settings.json; UPGRADE 2 → no artifact
change). Tests: declarative-reference-codebuddy (adapter/axes/fail-closed
negotiation + AC2 source-grep guard) + codebuddy-upgrades (live install asserts
all 4 extended hooks wired; dispatch.background survives negotiation above
baseline). Matrix + install-on-your-runtime updated; changeset (Changed).
capability-registry regenerated.

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

capabilities/codebuddy/capability.json

@@ -81,7 +81,12 @@
     "installSurface": "settings-json",
     "writesSharedSettings": true,
     "permissionWriter": null,
-    "extendedHookEvents": [],
+    "extendedHookEvents": [
+      "SubagentStop",
+      "Stop",
+      "PreCompact",
+      "SubagentStart"
+    ],
     "hostIntegration": {
       "embeddingMode": "declarative",
       "commandSurface": "slash-file",
@@ -98,6 +103,9 @@
       "stateIO": "filesystem",
       "transport": "mcp",
       "runtime": "node"
+    },
+    "hostBehaviors": {
+      "reportCommandsDir": true
     }
   }
 }