feat(#2092): migrate Qwen Code onto EoS imperative adapter + native subagents + SubagentStart (ADR-1239)

Fold all runtime==='qwen'/isQwen logic branches (skill-priority frontmatter,
branding/path rewrites, legacy commands/gsd cleanup, hyphen-namespace
normalization, RUNTIME_CONTENT_DISPATCH, hooks-surface label) into
descriptor-driven runtime.hostBehaviors on capabilities/qwen/capability.json,
read via _hostBehaviors(). Shared claude/qwen/hermes legacy-migration branches
in install-engine.cts folded to descriptor flags (claude+hermes descriptors
updated; FALLBACK_HOST_BEHAVIORS.claude floored). Byte-identical golden parity
for qwen/hermes/claude(global+local).

UPGRADE 1: native .qwen/agents/*.md subagent projection — new agents
artifact-layout kind + convertClaudeAgentToQwenAgent converter (name +
description + tools YAML block list; color/model dropped). qwen routed onto
the descriptor-driven agents path (_DESCRIPTOR_AGENTS_RUNTIMES).
UPGRADE 2: SubagentStart hook wired into extendedHookEvents + the
descriptor-gated hook-writer loop (activates only for qwen).

Tests: qwen-imperative-reference (adapter/axes/fail-closed/hostBehaviors +
no runtime==='qwen' source-grep across 4 files) + qwen-upgrades (agents file
validity + SubagentStart mirrors SubagentStop, descriptor-gated). Docs matrix
+ how-to updated; changeset added.

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

src/runtime-artifact-layout.cts

@@ -193,19 +193,27 @@ function agentsKind(destSubpath: string, prefix: string, configDir: string): Art
  * Agent filenames are preserved verbatim (the prefix is already embedded in the
  * agent stem — e.g. `gsd-planner.md`).
  *
- * #1173 SCOPE — plumbing only (declarations deferred): this provides the
- * converter dispatch + `isGlobal` scope threading for the descriptor's `agents`
- * kind, but NO runtime currently declares a converted `agents` kind in its
- * `capability.json`. The descriptor declarations for the 8 non-Claude runtimes
- * (copilot/antigravity/cursor/windsurf/augment/trae/codebuddy/cline) are
- * DEFERRED to a follow-up that first ships the ADR-1235 §0 byte-for-byte parity
- * harness, because the second `layout.kinds` consumer — `applySurface` /
- * `/gsd:surface` / `--materialize` (`src/surface.cts`) — does not yet mirror the
- * legacy agent pipeline (Copilot's `.agent.md` filename rename, the cross-cutting
- * path-prefix rewrite + attribution, stale-file cleanup, config-reading steps),
- * so declaring the kind now would regress the surface path. Until then the legacy
- * `bin/install.js` agent loop remains authoritative for the real install, and
- * this `convertedAgentsKind` is exercised only by synthetic-descriptor seam tests.
+ * #1173 SCOPE — plumbing only (real install still elsewhere): this provides
+ * the converter dispatch + `isGlobal` scope threading for the descriptor's
+ * `agents` kind. As of #2092, 8 non-Claude runtimes DO declare a converted
+ * `agents` kind in their `capability.json` — qwen (`convertClaudeAgentToQwenAgent`)
+ * plus the 7 that already declared one before it (antigravity, augment,
+ * codebuddy, copilot, cursor, trae, windsurf) — so the descriptor-level
+ * declaration is no longer deferred. What IS still deferred is wiring
+ * `resolveRuntimeArtifactLayout`'s `agents` kind into the REAL install:
+ * `bin/install.js`'s agent-staging loop does not consume this module's
+ * `convertedAgentsKind` resolution at all — it dispatches the very same
+ * converter functions directly via `_hostBehaviors(runtime)` checks
+ * (`frontmatterDialect`, `brandingRewrites`, `isCopilot`/`isAntigravity`/…),
+ * duplicating the mapping declared here. That duplication is deliberate until
+ * the second `layout.kinds` consumer — `applySurface` / `/gsd:surface` /
+ * `--materialize` (`src/surface.cts`) — mirrors the legacy agent pipeline
+ * (Copilot's `.agent.md` filename rename, the cross-cutting path-prefix
+ * rewrite + attribution, stale-file cleanup, config-reading steps); declaring
+ * `bin/install.js` itself against this resolver before then would risk
+ * regressing the surface path. Until that follow-up lands, `bin/install.js`
+ * remains authoritative for the real install, and this `convertedAgentsKind`
+ * is exercised only by `/gsd:surface` and synthetic-descriptor seam tests.
  *
  * Mirrors the `convertedCommandsKind` pattern (#785).
  *