feat(#3149): add dedicated init.debug entry point for /gsd:debug

/gsd:debug was one of the last workflows with no cmdInit* of its own: its
Step 0 made three separate round-trips (state.load, resolve-model
gsd-debugger, config-get workflow.tdd_mode) to assemble one context. Because
no debug-scoped fact was computed at any entry point, ADR-1671 admission gate
(2) could never be satisfied for debug — an applicability atom naming such a
fact would evaluate FALSE forever and silently exclude its section.

Adds cmdInitDebug (init.debug), registers it in the init router and the
command-alias table, and collapses debug.md Step 0 to one call. Every field
resolves through the same primitive the call it replaces used: loadConfig for
commit_docs, withProjectRoot for response_language (#2402), planningPaths for
debug_dir, resolveModelInternal for debugger_model, and the existing
Boolean(workflow.tdd_mode) idiom for tdd_mode.

PlanningPaths gains a debug field so state.load and init.debug share ONE
debug-directory expression rather than two kept in sync by hand. state.load
keeps emitting debug_dir: it is a shipped query surface with its own test
anchor, so narrowing it would break unseen consumers for no gain.

No WHEN_VOCABULARY atom and no gsd:section marker: gate (1), a consuming
section of at least 400 bytes, belongs to the change that adds the section.

Closes #3149

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/init-debug-workflow-contract.test.cjs

@@ -0,0 +1,87 @@
+// allow-test-rule: source-text-is-the-product (see #3149)
+// gsd-core/workflows/debug.md is shipped prompt content: the text IS what the
+// runtime loads, so its Step 0 contract can only be asserted against the text.
+// The behavioral half of this change lives in tests/init-debug.test.cjs, which
+// carries no exemption.
+
+'use strict';
+
+/**
+ * `debug.md` Step 0 contract after the `init.debug` consolidation (#3149).
+ *
+ * Matrix: `.gsd/phase/feat-3149-cmdinitdebug/50-test-matrix.md` group F.
+ *
+ * Guards the four ways this consolidation can silently regress:
+ *   F1/F2 — a replaced round-trip creeping back, or the new one being lost.
+ *   F3    — reading `config.response_language` (the nested state.load shape)
+ *           instead of the flat top-level field withProjectRoot injects. This
+ *           is the #2402 defect class: the workflow silently stays English.
+ *   F4    — losing the `@file:` unwrap, which large init payloads still need.
+ *   F5    — dropping the `section_manifest: null` -> read-everything rule,
+ *           without which a null manifest reads as "read nothing".
+ */
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const WORKFLOW_PATH = path.join(__dirname, '..', 'gsd-core', 'workflows', 'debug.md');
+const workflow = fs.readFileSync(WORKFLOW_PATH, 'utf-8');
+
+/** Every `gsd_run query <name>` invocation in the workflow, in document order. */
+function queryInvocations(text) {
+  return [...text.matchAll(/gsd_run query ([\w.-]+)/g)].map((m) => m[1]);
+}
+
+describe('debug.md Step 0 init contract (#3149, matrix §F)', () => {
+  test('calls init.debug exactly once (row F1)', () => {
+    const initDebugCalls = queryInvocations(workflow).filter((q) => q === 'init.debug');
+    assert.equal(initDebugCalls.length, 1, 'exactly one init.debug round-trip');
+  });
+
+  test('no longer makes the three replaced calls (row F2)', () => {
+    const queries = queryInvocations(workflow);
+
+    assert.equal(queries.includes('state.load'), false, 'state.load is replaced by init.debug');
+    assert.equal(
+      workflow.includes('resolve-model gsd-debugger'),
+      false,
+      'debugger_model now rides the init bundle'
+    );
+    assert.equal(
+      workflow.includes('config-get workflow.tdd_mode'),
+      false,
+      'tdd_mode now rides the init bundle'
+    );
+  });
+
+  test('reads the flat response_language, not the nested state.load shape (row F3)', () => {
+    assert.equal(
+      workflow.includes('config.response_language'),
+      false,
+      'withProjectRoot injects response_language at the TOP level; reading config.response_language ' +
+      'against an init bundle resolves undefined and silently drops translated output (#2402)'
+    );
+    assert.ok(
+      workflow.includes('`response_language`'),
+      'the field is still documented, just at its new location'
+    );
+  });
+
+  test('still unwraps an @file: payload (row F4)', () => {
+    assert.ok(
+      workflow.includes('@file:'),
+      'init payloads can spill to a file; dropping the unwrap leaves INIT holding a path, not JSON'
+    );
+  });
+
+  test('documents the null-manifest read-everything fallback (row F5)', () => {
+    assert.ok(workflow.includes('section_manifest'), 'the field is documented');
+    assert.ok(
+      /`null`[^\r\n]*read this workflow in full/i.test(workflow),
+      'a null section_manifest must be documented as "read everything" — without the rule, ' +
+      'a null manifest reads as an empty selection and the workflow reads nothing'
+    );
+  });
+});