fix(#2771): advisor mode spawns registered gsd-advisor-researcher subagent instead of general-purpose (#2884)

* test(#2771): advisor mode must spawn gsd-advisor-researcher, not general-purpose

* fix(#2771): spawn registered gsd-advisor-researcher subagent instead of general-purpose in advisor mode

universal-anti-patterns rule 10 (injected into discuss-phase via <required_reading>)
says NEVER use non-GSD agent types. The advisor mode spawned general-purpose and
manually told the agent to read the def — but gsd-advisor-researcher IS registered,
so spawning by type auto-loads it. Drop the manual-read prompt line (re-specifying
the def is a drift risk) and use the registered type.

* chore(#2771): changeset fragment (mentions follow-up #2883)

* test(#2771): widen manual-read-line regex to deny phrasing variants (review minor)

/read\s+@.*gsd-advisor-researcher\.md/i (case-insensitive, any 'read @' lead-in)
so a drift variant like 'Read @' or 'Load @' can't sneak the manual-def-read back in.

* chore(#2771): backfill changeset PR number (2884)

---------

Co-authored-by: Test <test@example.com>

.changeset/curious-pumas-wake.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 2886
+---
+**Discuss-phase advisor mode now spawns the registered `gsd-advisor-researcher` subagent instead of `general-purpose`** — resolving a contradiction with the universal-anti-patterns rule (injected into the same context) that forbids non-GSD agent types. The manual "read the agent def" prompt line is dropped (spawning by type auto-loads it). (#2771; the sibling assumptions-site needs a design decision — filed as #2883)

gsd-core/workflows/discuss-phase/modes/advisor.md

@@ -92,16 +92,14 @@ research agents.
 
    ```
    Agent(
-     prompt="First, read @~/.claude/agents/gsd-advisor-researcher.md for your role and instructions.
-
-     <gray_area>{area_name}: {area_description from gray area identification}</gray_area>
+     prompt="<gray_area>{area_name}: {area_description from gray area identification}</gray_area>
      <phase_context>{phase_goal and description from ROADMAP.md}</phase_context>
      <project_context>{project name and brief description from PROJECT.md}</project_context>
      <calibration_tier>{resolved calibration tier: full_maturity | standard | minimal_decisive}</calibration_tier>
 
      Research this gray area and return a structured comparison table with rationale.
      ${AGENT_SKILLS_ADVISOR}",
-     subagent_type="general-purpose",
+     subagent_type="gsd-advisor-researcher",
      model="{ADVISOR_MODEL}",
      description="Research: {area_name}"
    )

tests/issue-2771-advisor-subagent-type.test.cjs

@@ -0,0 +1,43 @@
+// allow-test-rule: structural-implementation-guard (#2771)
+'use strict';
+
+// Regression guard for #2771: the discuss-phase advisor mode must spawn the REGISTERED
+// `gsd-advisor-researcher` subagent (auto-loads the agent def), not `general-purpose` —
+// which contradicts universal-anti-patterns rule 10 (injected into discuss-phase via
+// <required_reading>): "NEVER use non-GSD agent types — ALWAYS use gsd-{agent}".
+// Spawning general-purpose + a manual "read the agent def" prompt re-specifies what the
+// def already owns (a drift risk; the same shape assumptions's answer_validation hit).
+
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const ADVISOR_MD = path.join(
+  __dirname, '..', 'gsd-core', 'workflows', 'discuss-phase', 'modes', 'advisor.md'
+);
+
+test('advisor mode spawns the registered gsd-advisor-researcher subagent, not general-purpose (#2771)', () => {
+  const src = fs.readFileSync(ADVISOR_MD, 'utf8');
+
+  // Locate the Agent() block that researches gray areas.
+  const agentIdx = src.indexOf('subagent_type=');
+  assert.ok(agentIdx !== -1, 'advisor.md must contain an Agent() subagent_type declaration');
+
+  assert.ok(
+    src.includes('subagent_type="gsd-advisor-researcher"'),
+    'advisor mode must spawn subagent_type="gsd-advisor-researcher" (the registered agent def auto-loads) — not general-purpose (#2771, universal-anti-patterns rule 10)'
+  );
+  assert.ok(
+    !src.includes('subagent_type="general-purpose"'),
+    'advisor mode must NOT spawn subagent_type="general-purpose" (contradicts universal-anti-patterns rule 10, injected into the same context) (#2771)'
+  );
+  // The manual "read @.../gsd-advisor-researcher.md" prompt line must be gone —
+  // spawning by type auto-loads the def; re-specifying it is a drift risk. Deny the
+  // full class (any "read @" lead-in, case-insensitive) so a phrasing variant can't
+  // sneak the drift back in.
+  assert.ok(
+    !/read\s+@.*gsd-advisor-researcher\.md/i.test(src),
+    'advisor mode must not manually instruct reading the agent def — spawning by type auto-loads it (#2771)'
+  );
+});