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>

docs/reference/host-integration-capability-matrix.md

@@ -427,6 +427,8 @@ Sources consulted:
 - https://www.codebuddy.ai/docs/cli/settings
 - /websites/codebuddy_cn (Context7)
 
+**EoS migration status (#2098):** Migrated onto the declarative adapter (dogfooded in `tests/declarative-reference-codebuddy.test.cjs`). The two remaining `isCodebuddy` branches in `bin/install.js` — a duplicate `commands/` slash-command output report, and a dead legacy agent-converter dispatch arm (unreachable since codebuddy is in `_DESCRIPTOR_AGENTS_RUNTIMES`) — were folded onto the already-generic `runtime.hostBehaviors.reportCommandsDir` (shared with Cursor) and removed outright; `isCodebuddy` no longer appears as a live read anywhere in `bin/install.js`, `src/runtime-artifact-conversion.cts`, `src/shell-command-projection.cts`, or `src/runtime-name-policy.cts`. Two upgrades land: (1) **extended hook events** — codebuddy's `extendedHookEvents` was previously `[]` (none wired); this PR wires all four — `SubagentStop`/`Stop`/`PreCompact`/`SubagentStart` — into `extendedHookEvents` (mirrors qwen/kimi), so an install now registers all four as hooks in `settings.json` alongside the pre-existing base session/tool events (`SessionStart`/`PreToolUse`/`PostToolUse`); cite https://www.codebuddy.ai/docs/cli/hooks. (2) **`dispatch.background`** — the descriptor already declared `true`, exceeding the `declarative-cli` profile baseline of `false`; the negotiation contract (`negotiateHostCapabilities`) now surfaces that value with no downgrade warning, documenting the legitimate deviation. Note: the CodeBuddy CLI has no background-dispatch frontmatter field on sub-agents (`agentMode`/`enabledAutoRun` are IDE-only per https://www.codebuddy.ai/docs/cli/sub-agents) — background dispatch remains a caller-side invocation parameter (`run_in_background: true`), not a field GSD's agent artifacts emit.
+
 ---
 
 ## copilot