diff --git a/.changeset/jolly-lynx-run.md b/.changeset/jolly-lynx-run.md
new file mode 100644
index 000000000..35028ad4a
--- /dev/null
+++ b/.changeset/jolly-lynx-run.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 3006
+---
+**Trae IDE is now detected as its own runtime** — `/gsd-new-project` and `/gsd-ingest-docs` no longer fall through to the Claude default when run inside Trae, and a `--trae` install no longer writes a malformed `.claude/.trae/rules/` or `.trae/.trae/rules/` instruction-file path; it now resolves to the concrete `.trae/rules/rules.md`. (#2658)
diff --git a/bin/install.js b/bin/install.js
index 26b3a8940..ff781806f 100755
--- a/bin/install.js
+++ b/bin/install.js
@@ -2701,10 +2701,55 @@ function convertClaudeToTraeMarkdown(content) {
   // Replace general-purpose subagent type with Trae's equivalent "general_purpose_task"
   converted = converted.replace(/subagent_type="general-purpose"/g, 'subagent_type="general_purpose_task"');
   converted = converted.replace(/\$ARGUMENTS\b/g, '{{GSD_ARGS}}');
-  converted = converted.replace(/`\.\/CLAUDE\.md`/g, '`.trae/rules/`');
-  converted = converted.replace(/\.\/CLAUDE\.md/g, '.trae/rules/');
-  converted = converted.replace(/`CLAUDE\.md`/g, '`.trae/rules/`');
-  converted = converted.replace(/\bCLAUDE\.md\b/g, '.trae/rules/');
+  // #2658: full-path forms (with a leading dot-claude-slash prefix) MUST be
+  // replaced before the bare Claude-instruction-file pattern and before the
+  // generic dot-claude-slash rewrite below — otherwise the bare pattern
+  // consumes only the instruction-filename tail, leaving that prefix stale
+  // in place, and the generic rewrite then mutates the stale leftover too,
+  // producing a doubled trae-prefix segment ahead of the rules path instead
+  // of a single clean one. (Deliberately never spelling the instruction
+  // filename as one contiguous "CLAUDE" + dot + "md" token, and never
+  // spelling either malformed shape out as a literal contiguous string, in
+  // ANY comment in this function: this file ships verbatim into local
+  // `--trae` installs, where it is itself run through this same class of
+  // find/replace — a literal instruction-filename token sitting in a
+  // comment gets "fixed" right along with real code, and the emitted-content
+  // regression test added alongside this fix asserts neither malformed
+  // shape appears anywhere in the installed tree, comments included; this
+  // bit the fix itself twice during development.) All forms converge on the
+  // same concrete file (never a bare directory) so this stays in parity
+  // with the `trae.js` RUNTIME_CONTENT_DISPATCH entry.
+  converted = converted.replace(/`\.\/\.claude\/CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\.\/\.claude\/CLAUDE\.md/g, '.trae/rules/rules.md');
+  converted = converted.replace(/`\.claude\/CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\.claude\/CLAUDE\.md/g, '.trae/rules/rules.md');
+  // #2658 (found via the end-to-end install regression test, not the static
+  // trace above): `copyWithPathReplacement` runs a GENERIC dot-claude-slash
+  // -> runtime-config-dir rewrite on every .md file before calling this
+  // converter — for `~/.claude/`, `$HOME/.claude/`, AND `./.claude/` alike —
+  // substituting a runtime-appropriate `pathPrefix` this function is never
+  // given and cannot itself compute (it differs per install invocation: a
+  // relative `./.trae/` for a project-local install, an arbitrary absolute
+  // path for a local install rooted elsewhere, `~/.trae/` for a global one).
+  // So for source using any of those prefixed forms, the patterns above
+  // never fire here — this converter only ever sees the ALREADY-rewritten
+  // "<runtime-config-dir>/" + instruction-filename shape, with whatever
+  // prefix the install actually used. The generic pattern below preserves
+  // that prefix verbatim (via the capture group) and only fixes the
+  // filename suffix, rather than assuming a fixed `./.trae/` shape — a
+  // narrower fixed-prefix version of this pattern shipped first and still
+  // left the doubled-prefix defect live for the `$HOME/.claude/` and
+  // `~/.claude/` forms specifically (found the same way, one regression-test
+  // run later). Scoped to a `.trae/` tail so it cannot also swallow the
+  // unprefixed `./CLAUDE.md` form the very next pattern handles differently
+  // (discarding the prefix entirely, not preserving it). Must run before
+  // the bare pattern for the same consume-the-full-match-first reason.
+  converted = converted.replace(/`([^\s`]*\.trae\/)CLAUDE\.md`/g, '`$1rules/rules.md`');
+  converted = converted.replace(/([^\s`]*\.trae\/)CLAUDE\.md/g, '$1rules/rules.md');
+  converted = converted.replace(/`\.\/CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\.\/CLAUDE\.md/g, '.trae/rules/rules.md');
+  converted = converted.replace(/`CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\bCLAUDE\.md\b/g, '.trae/rules/rules.md');
   converted = converted.replace(/\.claude\/skills\//g, '.trae/skills/');
   converted = converted.replace(/\.\/\.claude\//g, './.trae/');
   converted = converted.replace(/\.claude\//g, '.trae/');
@@ -7525,7 +7570,18 @@ const RUNTIME_CONTENT_DISPATCH = {
         return `/gsd-${commandName}`;
       });
       content = content.replace(/\.claude\/skills\//g, '.trae/skills/');
-      content = content.replace(/CLAUDE\.md/g, '.trae/rules/');
+      // #2658: the full dot-claude-slash-prefixed instruction-file path must
+      // be replaced before the bare instruction-filename fallback, or the
+      // bare regex only rewrites that filename and leaves the prefix stale
+      // in place, producing a malformed doubled-prefix path (see the longer
+      // note in convertClaudeToTraeMarkdown above — the instruction filename
+      // and either malformed shape are deliberately never spelled out
+      // contiguously here either, for the same reason: this file ships
+      // verbatim). Both forms target the same concrete file (never a bare
+      // directory), matching the `.md` converter (convertClaudeToTraeMarkdown)
+      // so js/cjs and md content agree on one canonical path.
+      content = content.replace(/\.claude\/CLAUDE\.md/g, '.trae/rules/rules.md');
+      content = content.replace(/CLAUDE\.md/g, '.trae/rules/rules.md');
       content = content.replace(/\bClaude Code\b/g, 'Trae');
       return content;
     },
diff --git a/capabilities/trae/capability.json b/capabilities/trae/capability.json
index af4dfea03..c4c39d4e3 100644
--- a/capabilities/trae/capability.json
+++ b/capabilities/trae/capability.json
@@ -86,7 +86,8 @@
     },
     "hostBehaviors": {
       "skipSharedHooksInstall": true,
-      "soloStageMetadata": "workflow"
+      "soloStageMetadata": "workflow",
+      "projectInstructionFile": ".trae/rules/rules.md"
     }
   }
 }
diff --git a/gsd-core/bin/lib/capability-registry.cjs b/gsd-core/bin/lib/capability-registry.cjs
index b8671555f..694c11d09 100644
--- a/gsd-core/bin/lib/capability-registry.cjs
+++ b/gsd-core/bin/lib/capability-registry.cjs
@@ -3384,7 +3384,8 @@ const capabilities = {
       },
       "hostBehaviors": {
         "skipSharedHooksInstall": true,
-        "soloStageMetadata": "workflow"
+        "soloStageMetadata": "workflow",
+        "projectInstructionFile": ".trae/rules/rules.md"
       }
     }
   },
@@ -6612,7 +6613,8 @@ const runtimes = {
       },
       "hostBehaviors": {
         "skipSharedHooksInstall": true,
-        "soloStageMetadata": "workflow"
+        "soloStageMetadata": "workflow",
+        "projectInstructionFile": ".trae/rules/rules.md"
       }
     }
   },
diff --git a/gsd-core/workflows/ingest-docs.md b/gsd-core/workflows/ingest-docs.md
index 5261d94d0..e6a81341b 100644
--- a/gsd-core/workflows/ingest-docs.md
+++ b/gsd-core/workflows/ingest-docs.md
@@ -84,9 +84,10 @@ git init
 - execution_context path `/.codex/` → `RUNTIME=codex`
 - `/.gemini/` → `RUNTIME=gemini`
 - `/.opencode/` or `/.config/opencode/` → `RUNTIME=opencode`
+- `/.trae/` → `RUNTIME=trae`
 - else → `RUNTIME=claude`
 
-Fall back to env vars (`CODEX_HOME`, `GEMINI_CONFIG_DIR`, `OPENCODE_CONFIG_DIR`) if execution_context is unavailable.
+Fall back to env vars (`CODEX_HOME`, `GEMINI_CONFIG_DIR`, `OPENCODE_CONFIG_DIR`, `TRAE_CONFIG_DIR`) if execution_context is unavailable.
 
 </step>
 
diff --git a/gsd-core/workflows/new-project.md b/gsd-core/workflows/new-project.md
index 974c5f344..02d209ddb 100644
--- a/gsd-core/workflows/new-project.md
+++ b/gsd-core/workflows/new-project.md
@@ -101,6 +101,7 @@ Derive `RUNTIME` from the invoking prompt's `execution_context` path:
 - Path contains `/.codex/` → `RUNTIME=codex`
 - Path contains `/.gemini/` → `RUNTIME=gemini`
 - Path contains `/.config/opencode/` or `/.opencode/` → `RUNTIME=opencode`
+- Path contains `/.trae/` → `RUNTIME=trae`
 - Otherwise → `RUNTIME=claude`
 
 If `execution_context` path is not available, fall back to env vars:
@@ -108,6 +109,7 @@ If `execution_context` path is not available, fall back to env vars:
 if [ -n "$CODEX_HOME" ]; then RUNTIME="codex"
 elif [ -n "$GEMINI_CONFIG_DIR" ]; then RUNTIME="gemini"
 elif [ -n "$OPENCODE_CONFIG_DIR" ] || [ -n "$OPENCODE_CONFIG" ]; then RUNTIME="opencode"
+elif [ -n "$TRAE_CONFIG_DIR" ]; then RUNTIME="trae"
 else RUNTIME="claude"; fi
 ```
 
diff --git a/src/runtime-artifact-conversion.cts b/src/runtime-artifact-conversion.cts
index 44de4d78d..95f0c4acd 100644
--- a/src/runtime-artifact-conversion.cts
+++ b/src/runtime-artifact-conversion.cts
@@ -1311,10 +1311,55 @@ function convertClaudeToTraeMarkdown(content) {
   // Replace general-purpose subagent type with Trae's equivalent "general_purpose_task"
   converted = converted.replace(/subagent_type="general-purpose"/g, 'subagent_type="general_purpose_task"');
   converted = converted.replace(/\$ARGUMENTS\b/g, '{{GSD_ARGS}}');
-  converted = converted.replace(/`\.\/CLAUDE\.md`/g, '`.trae/rules/`');
-  converted = converted.replace(/\.\/CLAUDE\.md/g, '.trae/rules/');
-  converted = converted.replace(/`CLAUDE\.md`/g, '`.trae/rules/`');
-  converted = converted.replace(/\bCLAUDE\.md\b/g, '.trae/rules/');
+  // #2658: full-path forms (with a leading dot-claude-slash prefix) MUST be
+  // replaced before the bare Claude-instruction-file pattern and before the
+  // generic dot-claude-slash rewrite below — otherwise the bare pattern
+  // consumes only the instruction-filename tail, leaving that prefix stale
+  // in place, and the generic rewrite then mutates the stale leftover too,
+  // producing a doubled trae-prefix segment ahead of the rules path instead
+  // of a single clean one. (Deliberately never spelling the instruction
+  // filename as one contiguous "CLAUDE" + dot + "md" token, and never
+  // spelling either malformed shape out as a literal contiguous string, in
+  // ANY comment in this function: this file ships verbatim into local
+  // `--trae` installs, where it is itself run through this same class of
+  // find/replace — a literal instruction-filename token sitting in a
+  // comment gets "fixed" right along with real code, and the emitted-content
+  // regression test added alongside this fix asserts neither malformed
+  // shape appears anywhere in the installed tree, comments included; this
+  // bit the fix itself twice during development.) All forms converge on the
+  // same concrete file (never a bare directory) so this stays in parity
+  // with the `trae.js` RUNTIME_CONTENT_DISPATCH entry.
+  converted = converted.replace(/`\.\/\.claude\/CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\.\/\.claude\/CLAUDE\.md/g, '.trae/rules/rules.md');
+  converted = converted.replace(/`\.claude\/CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\.claude\/CLAUDE\.md/g, '.trae/rules/rules.md');
+  // #2658 (found via the end-to-end install regression test, not the static
+  // trace above): `copyWithPathReplacement` runs a GENERIC dot-claude-slash
+  // -> runtime-config-dir rewrite on every .md file before calling this
+  // converter — for `~/.claude/`, `$HOME/.claude/`, AND `./.claude/` alike —
+  // substituting a runtime-appropriate `pathPrefix` this function is never
+  // given and cannot itself compute (it differs per install invocation: a
+  // relative `./.trae/` for a project-local install, an arbitrary absolute
+  // path for a local install rooted elsewhere, `~/.trae/` for a global one).
+  // So for source using any of those prefixed forms, the patterns above
+  // never fire here — this converter only ever sees the ALREADY-rewritten
+  // "<runtime-config-dir>/" + instruction-filename shape, with whatever
+  // prefix the install actually used. The generic pattern below preserves
+  // that prefix verbatim (via the capture group) and only fixes the
+  // filename suffix, rather than assuming a fixed `./.trae/` shape — a
+  // narrower fixed-prefix version of this pattern shipped first and still
+  // left the doubled-prefix defect live for the `$HOME/.claude/` and
+  // `~/.claude/` forms specifically (found the same way, one regression-test
+  // run later). Scoped to a `.trae/` tail so it cannot also swallow the
+  // unprefixed `./CLAUDE.md` form the very next pattern handles differently
+  // (discarding the prefix entirely, not preserving it). Must run before
+  // the bare pattern for the same consume-the-full-match-first reason.
+  converted = converted.replace(/`([^\s`]*\.trae\/)CLAUDE\.md`/g, '`$1rules/rules.md`');
+  converted = converted.replace(/([^\s`]*\.trae\/)CLAUDE\.md/g, '$1rules/rules.md');
+  converted = converted.replace(/`\.\/CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\.\/CLAUDE\.md/g, '.trae/rules/rules.md');
+  converted = converted.replace(/`CLAUDE\.md`/g, '`.trae/rules/rules.md`');
+  converted = converted.replace(/\bCLAUDE\.md\b/g, '.trae/rules/rules.md');
   converted = converted.replace(/\.claude\/skills\//g, '.trae/skills/');
   converted = converted.replace(/\.\/\.claude\//g, './.trae/');
   converted = converted.replace(/\.claude\//g, '.trae/');
diff --git a/tests/emitted-drift-acks/2658-trae-instruction-file-path.json b/tests/emitted-drift-acks/2658-trae-instruction-file-path.json
new file mode 100644
index 000000000..83f2f5e8d
--- /dev/null
+++ b/tests/emitted-drift-acks/2658-trae-instruction-file-path.json
@@ -0,0 +1,30 @@
+{
+  "version": 1,
+  "paths": {
+    "gsd-core/references/checkpoints.md": "#2658: mentions CLAUDE.md in prose. convertClaudeToTraeMarkdown's CLAUDE.md replacement target changed from the bare directory '.trae/rules/' to the concrete file '.trae/rules/rules.md' for every CLAUDE.md mention (bare, ./-prefixed, backtick-wrapped, and the buggy .claude/-prefixed form that previously produced a malformed doubled path) — so trae-emitted output differs for every file that mentions CLAUDE.md, not only the ones that hit the reported bug. Content is otherwise byte-identical.",
+    "gsd-core/references/debugger-bug-taxonomy.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/references/debugger-fix-acceptance.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/references/debugger-repro-hardening.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/references/debugger-sbfl.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/references/git-integration.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/references/planner-human-verify-mode.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/templates/README.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/templates/claude-md.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/templates/codebase/structure.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/execute-phase.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/execute-plan.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/help/modes/full.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/milestone-summary.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/plan-phase.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/profile-user.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/progress.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/quick.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/sketch-wrap-up.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/spike-wrap-up.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "gsd-core/workflows/update.md": "#2658: same CLAUDE.md replacement-target change as checkpoints.md above (bare directory '.trae/rules/' -> concrete file '.trae/rules/rules.md').",
+    "skills/gsd-ns-project/skills/profile-user/SKILL.md": "#2658: derived (via commands/gsd/profile-user.md, which mentions CLAUDE.md) through convertClaudeToTraeMarkdown; same replacement-target change as checkpoints.md above.",
+    "skills/gsd-ns-review/skills/code-review/SKILL.md": "#2658: derived (via commands/gsd/code-review.md, which mentions CLAUDE.md) through convertClaudeToTraeMarkdown; same replacement-target change as checkpoints.md above.",
+    "ingest-docs.md": "#2658: runtime-detection block gained a `/.trae/` path-based line and a `TRAE_CONFIG_DIR` env-var fallback line (the same trae-detection gap found in new-project.md, fixed here too since it is the identical defect in a sibling workflow).",
+    "new-project.md": "#2658: runtime-detection block gained a `/.trae/` path-based line and a `TRAE_CONFIG_DIR` env-var fallback line, so trae resolves to RUNTIME=trae instead of falling through to the claude default."
+  }
+}
diff --git a/tests/fix-2658-trae-runtime-detection-and-instruction-path.test.cjs b/tests/fix-2658-trae-runtime-detection-and-instruction-path.test.cjs
new file mode 100644
index 000000000..0da6ae3c3
--- /dev/null
+++ b/tests/fix-2658-trae-runtime-detection-and-instruction-path.test.cjs
@@ -0,0 +1,255 @@
+'use strict';
+
+/**
+ * Regression tests for #2658 — Trae runtime not detected in workflow
+ * runtime-detection blocks (falls back to claude), and the install-time
+ * `CLAUDE.md` path rewrite mutilates the claude fallback into a malformed
+ * path instead of resolving to the Trae rules file.
+ *
+ * Defects collided (see
+ * .gsd/bug/fix-2658-trae-runtime-not-detected-falls-back-to-/10-diagnosis.md):
+ *
+ *   1. `gsd-core/workflows/new-project.md` AND `gsd-core/workflows/ingest-docs.md`
+ *      (found during this remediation — same pattern, same gap, not just
+ *      new-project.md as originally reported) never recognized trae (path
+ *      `/.trae/` or env `TRAE_CONFIG_DIR`) in their runtime-detection blocks —
+ *      fell through to `RUNTIME=claude`.
+ *   2. The `trae.js` entry in `bin/install.js`'s `RUNTIME_CONTENT_DISPATCH`
+ *      replaced bare `CLAUDE.md` first, leaving a stale `.claude/` prefix:
+ *      `.claude/CLAUDE.md` -> `.claude/.trae/rules/`.
+ *   3. `convertClaudeToTraeMarkdown` (mirrored in `bin/install.js` and
+ *      `src/runtime-artifact-conversion.cts`) had the same class of bug but a
+ *      DIFFERENT wrong output (`.trae/.trae/rules/`), because its generic
+ *      `.claude/` -> `.trae/` rewrite ran after the bare `CLAUDE.md` rewrite
+ *      and re-mutated the leftover prefix.
+ *   4. `capabilities/trae/capability.json` didn't declare
+ *      `hostBehaviors.projectInstructionFile`, so even a correctly-detected
+ *      trae runtime resolved to the generic `AGENTS.md` default via
+ *      `getProjectInstructionFile`.
+ *   5. Found by the end-to-end install test below, one level deeper than the
+ *      static trace: `copyWithPathReplacement` (bin/install.js) runs a
+ *      GENERIC `~/.claude/` / `$HOME/.claude/` / `./.claude/` -> runtime-dir
+ *      rewrite on every .md file BEFORE calling `convertClaudeToTraeMarkdown`,
+ *      substituting a `pathPrefix` the converter is never given (it differs
+ *      per install: relative for a project-local install, an arbitrary
+ *      absolute path for a local install rooted elsewhere, `~/.trae/` for a
+ *      global one). The converter's `.claude/CLAUDE.md`-specific patterns
+ *      (defect 3's fix) never fire on that already-rewritten text, and the
+ *      bare fallback still doubles the prefix — a first attempt at fixing
+ *      this handled only the `./.trae/CLAUDE.md` shape and missed the
+ *      `~/.claude/` / `$HOME/.claude/` forms `gsd-core/workflows/profile-user.md`
+ *      actually uses, caught by row 12 (the real spawned install) below on a
+ *      second run. Fixed with a prefix-preserving pattern (capture whatever
+ *      precedes a `.trae/` tail, keep it, fix only the filename suffix)
+ *      instead of assuming one fixed shape.
+ */
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const fc = require('fast-check');
+
+process.env['GSD_TEST_MODE'] = '1';
+
+const { getProjectInstructionFile } = require('../gsd-core/bin/lib/runtime-name-policy.cjs');
+const { convertClaudeToTraeMarkdown } = require('../bin/install.js');
+const runtimeArtifactConversion = require('../gsd-core/bin/lib/runtime-artifact-conversion.cjs');
+
+const { runMinimalInstall, walk } = require('./helpers/install-shared.cjs');
+const { cleanup } = require('./helpers.cjs');
+
+const REPO_ROOT = path.join(__dirname, '..');
+const MALFORMED_SINGLE = '.claude/.trae/rules';
+const MALFORMED_DOUBLE = '.trae/.trae/rules';
+const EXPECTED_PATH = '.trae/rules/rules.md';
+
+describe('#2658 acceptance criterion 2: getProjectInstructionFile resolves trae to a concrete file', () => {
+  test('trae maps to .trae/rules/rules.md (not the generic AGENTS.md default)', () => {
+    assert.strictEqual(getProjectInstructionFile('trae'), EXPECTED_PATH);
+  });
+
+  test('capability descriptor declares the same path getProjectInstructionFile returns', () => {
+    const cap = JSON.parse(
+      fs.readFileSync(path.join(REPO_ROOT, 'capabilities', 'trae', 'capability.json'), 'utf8'),
+    );
+    assert.strictEqual(cap.runtime.hostBehaviors.projectInstructionFile, EXPECTED_PATH);
+    assert.strictEqual(getProjectInstructionFile('trae'), cap.runtime.hostBehaviors.projectInstructionFile);
+  });
+
+  test('the declared path is a concrete file, not a bare directory (acceptance criterion 2)', () => {
+    assert.ok(!EXPECTED_PATH.endsWith('/'), 'must not be directory-terminated');
+    assert.ok(/\.md$/.test(EXPECTED_PATH), 'must name a concrete markdown file');
+  });
+});
+
+describe('#2658: convertClaudeToTraeMarkdown never mutilates the CLAUDE.md path (bin/install.js)', () => {
+  const cases = [
+    ['bare CLAUDE.md', 'See CLAUDE.md for details.'],
+    ['./CLAUDE.md', 'Read ./CLAUDE.md before starting.'],
+    ['backtick-wrapped `CLAUDE.md`', 'The file `CLAUDE.md` is authoritative.'],
+    ['the exact reported-bug input: .claude/CLAUDE.md', 'Fallback path is .claude/CLAUDE.md by default.'],
+    ['backtick-wrapped .claude/CLAUDE.md', 'Fallback: `.claude/CLAUDE.md`.'],
+    ['./.claude/CLAUDE.md', 'From root: ./.claude/CLAUDE.md'],
+  ];
+  for (const [label, input] of cases) {
+    test(`${label} -> ${EXPECTED_PATH}, no malformed output`, () => {
+      const out = convertClaudeToTraeMarkdown(input);
+      assert.ok(!out.includes(MALFORMED_SINGLE), `output must not contain "${MALFORMED_SINGLE}": ${out}`);
+      assert.ok(!out.includes(MALFORMED_DOUBLE), `output must not contain "${MALFORMED_DOUBLE}": ${out}`);
+      assert.ok(out.includes(EXPECTED_PATH), `output must contain "${EXPECTED_PATH}": ${out}`);
+    });
+  }
+
+  test('fast-check property: any surrounding text around .claude/CLAUDE.md never yields a malformed path', () => {
+    fc.assert(
+      fc.property(
+        fc.string({ maxLength: 40 }),
+        fc.string({ maxLength: 40 }),
+        (prefix, suffix) => {
+          const content = `${prefix}.claude/CLAUDE.md${suffix}`;
+          const out = convertClaudeToTraeMarkdown(content);
+          assert.ok(!out.includes(MALFORMED_SINGLE));
+          assert.ok(!out.includes(MALFORMED_DOUBLE));
+        },
+      ),
+      { numRuns: 200 },
+    );
+  });
+});
+
+describe('#2658 defect 5: post-generic-rewrite ".trae/"-prefixed forms preserve their prefix instead of doubling it', () => {
+  // These simulate the text `copyWithPathReplacement`'s generic `~/.claude/` /
+  // `$HOME/.claude/` / `./.claude/` -> runtime-dir pass hands to
+  // convertClaudeToTraeMarkdown — the converter never sees the original
+  // `.claude/`-prefixed source in this pipeline, only these already-rewritten
+  // shapes. A fixed-shape patch that only handled the local relative form
+  // left the local-install-absolute-path and global tilde forms broken.
+  const cases = [
+    ['local relative (post "./.claude/" -> "./.trae/" rewrite)', './.trae/CLAUDE.md', './.trae/rules/rules.md'],
+    [
+      'local install absolute path (post "./.claude/" -> "<tmp-root>/.trae/" rewrite)',
+      '/private/var/folders/xx/gsd-trae-local-abc123/.trae/CLAUDE.md',
+      '/private/var/folders/xx/gsd-trae-local-abc123/.trae/rules/rules.md',
+    ],
+    ['global tilde (post "~/.claude/" -> "~/.trae/" rewrite)', '~/.trae/CLAUDE.md', '~/.trae/rules/rules.md'],
+    ['backtick-wrapped local relative', '`./.trae/CLAUDE.md`', '`./.trae/rules/rules.md`'],
+  ];
+  for (const [label, input, expected] of cases) {
+    test(`${label} -> prefix preserved, no malformed path`, () => {
+      const out = convertClaudeToTraeMarkdown(input);
+      assert.ok(!out.includes(MALFORMED_SINGLE), `output must not contain "${MALFORMED_SINGLE}": ${out}`);
+      assert.ok(!out.includes(MALFORMED_DOUBLE), `output must not contain "${MALFORMED_DOUBLE}": ${out}`);
+      assert.strictEqual(out, expected);
+    });
+  }
+
+  test('fast-check property: any arbitrary path ending in .trae/ never yields a doubled prefix', () => {
+    fc.assert(
+      fc.property(
+        fc.string({ maxLength: 30 }).filter((s) => !s.includes('`') && !/\s/.test(s)),
+        (prefix) => {
+          const content = `${prefix}.trae/CLAUDE.md`;
+          const out = convertClaudeToTraeMarkdown(content);
+          assert.ok(!out.includes(MALFORMED_SINGLE));
+          assert.ok(!out.includes(MALFORMED_DOUBLE));
+        },
+      ),
+      { numRuns: 200 },
+    );
+  });
+});
+
+describe('#2658 output parity: bin/install.js vs runtime-artifact-conversion.cjs convertClaudeToTraeMarkdown (#2094 mirror)', () => {
+  // Parity must hold for the pre-existing reported-bug input AND for every
+  // arbitrary-prefix ".trae/"-tail shape the prefix-preserving regex
+  // (bin/install.js:2747-2748, mirrored byte-for-byte at
+  // src/runtime-artifact-conversion.cts:1357-1358) was added to handle. A
+  // change to only one copy of that regex would otherwise pass every other
+  // test in this file — none of the defect-5 cases above call the mirror —
+  // while silently diverging from the other copy.
+  const parityCases = [
+    ['the reported-bug input (bare .claude/ prefix)', 'Fallback path is .claude/CLAUDE.md by default.'],
+    ['local relative prefix (post "./.claude/" -> "./.trae/" rewrite)', './.trae/CLAUDE.md'],
+    [
+      'nested project-path absolute prefix (post "./.claude/" -> "<tmp-root>/.trae/" rewrite)',
+      '/private/var/folders/xx/gsd-trae-local-abc123/.trae/CLAUDE.md',
+    ],
+    ['global tilde prefix (post "~/.claude/" -> "~/.trae/" rewrite)', '~/.trae/CLAUDE.md'],
+    ['$HOME-variable prefix (post "$HOME/.claude/" -> "$HOME/.trae/" rewrite)', '$HOME/.trae/CLAUDE.md'],
+    ['backtick-wrapped local relative prefix', '`./.trae/CLAUDE.md`'],
+  ];
+
+  for (const [label, input] of parityCases) {
+    test(`identical output for ${label}`, () => {
+      assert.strictEqual(
+        convertClaudeToTraeMarkdown(input),
+        runtimeArtifactConversion.convertClaudeToTraeMarkdown(input),
+      );
+    });
+  }
+
+  test('fast-check property: any arbitrary ".trae/"-tail path produces identical output in both implementations', () => {
+    fc.assert(
+      fc.property(
+        fc.string({ maxLength: 30 }).filter((s) => !s.includes('`') && !/\s/.test(s)),
+        (prefix) => {
+          const content = `${prefix}.trae/CLAUDE.md`;
+          assert.strictEqual(
+            convertClaudeToTraeMarkdown(content),
+            runtimeArtifactConversion.convertClaudeToTraeMarkdown(content),
+          );
+        },
+      ),
+      { numRuns: 200 },
+    );
+  });
+});
+
+describe('#2658: end-to-end --trae install never emits the malformed path (acceptance criterion 1)', () => {
+  test('local install: no emitted .md/.js/.cjs file contains the malformed strings; the rules file is concrete', () => {
+    const { configDir, root } = runMinimalInstall({ runtime: 'trae', scope: 'local' });
+    try {
+      const files = walk(configDir).filter((f) => /\.(md|js|cjs)$/.test(f));
+      assert.ok(files.length > 0, 'expected at least one emitted .md/.js/.cjs file');
+      for (const file of files) {
+        const content = fs.readFileSync(file, 'utf8');
+        assert.ok(!content.includes(MALFORMED_SINGLE), `${file} must not contain "${MALFORMED_SINGLE}"`);
+        assert.ok(!content.includes(MALFORMED_DOUBLE), `${file} must not contain "${MALFORMED_DOUBLE}"`);
+      }
+    } finally {
+      cleanup(root);
+    }
+  });
+});
+
+describe('#2658 acceptance criterion 3: new-project.md / ingest-docs.md detect trae before falling back to claude', () => {
+  const workflowsDir = path.join(REPO_ROOT, 'gsd-core', 'workflows');
+
+  test('new-project.md recognizes /.trae/ path and TRAE_CONFIG_DIR before the claude fallback', () => {
+    const content = fs.readFileSync(path.join(workflowsDir, 'new-project.md'), 'utf8');
+    const pathBlock = content.match(/Derive `RUNTIME`[\s\S]*?Otherwise → `RUNTIME=claude`/);
+    assert.ok(pathBlock, 'runtime-detection path block must exist');
+    assert.ok(
+      /Path contains `\/\.trae\/` → `RUNTIME=trae`/.test(pathBlock[0]),
+      'path-based detection must recognize /.trae/ before the claude fallback',
+    );
+    const envBlock = content.match(/if \[ -n "\$CODEX_HOME" \][\s\S]*?else RUNTIME="claude"; fi/);
+    assert.ok(envBlock, 'env-var fallback block must exist');
+    assert.ok(
+      /TRAE_CONFIG_DIR/.test(envBlock[0]),
+      'env-var fallback must recognize TRAE_CONFIG_DIR before the claude fallback',
+    );
+  });
+
+  test('ingest-docs.md carries the same trae detection (found during this remediation, not just new-project.md)', () => {
+    const content = fs.readFileSync(path.join(workflowsDir, 'ingest-docs.md'), 'utf8');
+    const block = content.match(/\*\*Detect runtime\*\*[\s\S]*?else → `RUNTIME=claude`/);
+    assert.ok(block, 'runtime-detection block must exist');
+    assert.ok(
+      /`\/\.trae\/` → `RUNTIME=trae`/.test(block[0]),
+      'ingest-docs.md must also recognize /.trae/ before the claude fallback',
+    );
+    assert.ok(/TRAE_CONFIG_DIR/.test(content), 'env-var fallback mention must include TRAE_CONFIG_DIR');
+  });
+});