fix(query/agent-skills): emit raw <agent_skills> block instead of JSON-wrapped string (#2917)

* fix(query/agent-skills): emit raw <agent_skills> block instead of JSON-wrapped string

The CLI dispatcher (`cli.ts`) JSON-stringifies all query handler results via
`console.log(JSON.stringify(result.data, null, 2))`.  For the `agent-skills`
handler this produced a JSON-quoted string literal — e.g.
`"<agent_skills>\n…</agent_skills>"` — which workflows embedded verbatim via
`$(gsd-sdk query agent-skills gsd-planner)`, breaking all `<agent_skills>`
injection into spawned subagent prompts.

Fix: add an optional `format: 'json' | 'text'` field to `QueryResult`.  When a
handler returns `format: 'text'` and `--pick` is not active, the CLI writes the
string directly via `process.stdout.write` instead of JSON-stringifying it.
`agentSkills` sets `format: 'text'` for non-empty blocks.

Regression guard: two new CLI integration tests in `skills.test.ts` spawn the
CLI as a child process and assert that (a) a mapped agent type receives the raw
XML block on stdout and (b) an unmapped agent type produces the existing JSON
empty-string output.

Fixes #2914.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* docs(changelog): add #2917 entry under Unreleased Fixed

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

sdk/src/query/utils.ts

@@ -24,6 +24,16 @@ import { GSDError, ErrorClassification } from '../errors.js';
 /** Structured result returned by all query handlers. */
 export interface QueryResult<T = unknown> {
   data: T;
+  /**
+   * Output format hint for the CLI dispatcher.
+   * `'text'` — write `data` as-is to stdout (no JSON-stringify).
+   * `'json'` (default) — JSON-stringify as usual.
+   *
+   * Only meaningful when `data` is a string and the consumer is the CLI.
+   * Used by `agent-skills` so workflows embedding `$(gsd-sdk query …)` receive
+   * a raw `<agent_skills>` XML block rather than a JSON-quoted string.
+   */
+  format?: 'json' | 'text';
 }
 
 /** Signature for a query handler function. */