feat: add WSL environment hint to system prompt (#8285)

When running inside WSL (Windows Subsystem for Linux), inject a hint into
the system prompt explaining that the Windows host filesystem is mounted
at /mnt/c/, /mnt/d/, etc. This lets the agent naturally translate Windows
paths (Desktop, Documents) to their /mnt/ equivalents without the user
needing to configure anything.

Uses the existing is_wsl() detection from hermes_constants (cached,
checks /proc/version for 'microsoft'). Adds build_environment_hints()
in prompt_builder.py — extensible for Termux, Docker, etc. later.

Closes the UX gap where WSL users had to manually explain path
translation to the agent every session.

agent/prompt_builder.py

@@ -12,7 +12,7 @@ import threading
 from collections import OrderedDict
 from pathlib import Path
 
-from hermes_constants import get_hermes_home, get_skills_dir
+from hermes_constants import get_hermes_home, get_skills_dir, is_wsl
 from typing import Optional
 
 from agent.skill_utils import (
@@ -366,6 +366,36 @@ PLATFORM_HINTS = {
     ),
 }
 
+# ---------------------------------------------------------------------------
+# Environment hints — execution-environment awareness for the agent.
+# Unlike PLATFORM_HINTS (which describe the messaging channel), these describe
+# the machine/OS the agent's tools actually run on.
+# ---------------------------------------------------------------------------
+
+WSL_ENVIRONMENT_HINT = (
+    "You are running inside WSL (Windows Subsystem for Linux). "
+    "The Windows host filesystem is mounted under /mnt/ — "
+    "/mnt/c/ is the C: drive, /mnt/d/ is D:, etc. "
+    "The user's Windows files are typically at "
+    "/mnt/c/Users/<username>/Desktop/, Documents/, Downloads/, etc. "
+    "When the user references Windows paths or desktop files, translate "
+    "to the /mnt/c/ equivalent. You can list /mnt/c/Users/ to discover "
+    "the Windows username if needed."
+)
+
+
+def build_environment_hints() -> str:
+    """Return environment-specific guidance for the system prompt.
+
+    Detects WSL, and can be extended for Termux, Docker, etc.
+    Returns an empty string when no special environment is detected.
+    """
+    hints: list[str] = []
+    if is_wsl():
+        hints.append(WSL_ENVIRONMENT_HINT)
+    return "\n\n".join(hints)
+
+
 CONTEXT_FILE_MAX_CHARS = 20_000
 CONTEXT_TRUNCATE_HEAD_RATIO = 0.7
 CONTEXT_TRUNCATE_TAIL_RATIO = 0.2

run_agent.py

@@ -94,7 +94,7 @@ from agent.model_metadata import (
 from agent.context_compressor import ContextCompressor
 from agent.subdirectory_hints import SubdirectoryHintTracker
 from agent.prompt_caching import apply_anthropic_cache_control
-from agent.prompt_builder import build_skills_system_prompt, build_context_files_prompt, load_soul_md, TOOL_USE_ENFORCEMENT_GUIDANCE, TOOL_USE_ENFORCEMENT_MODELS, DEVELOPER_ROLE_MODELS, GOOGLE_MODEL_OPERATIONAL_GUIDANCE, OPENAI_MODEL_EXECUTION_GUIDANCE
+from agent.prompt_builder import build_skills_system_prompt, build_context_files_prompt, build_environment_hints, load_soul_md, TOOL_USE_ENFORCEMENT_GUIDANCE, TOOL_USE_ENFORCEMENT_MODELS, DEVELOPER_ROLE_MODELS, GOOGLE_MODEL_OPERATIONAL_GUIDANCE, OPENAI_MODEL_EXECUTION_GUIDANCE
 from agent.usage_pricing import estimate_usage_cost, normalize_usage
 from agent.display import (
     KawaiiSpinner, build_tool_preview as _build_tool_preview,
@@ -3193,6 +3193,12 @@ class AIAgent:
                 f"not on any model name returned by the API."
             )
 
+        # Environment hints (WSL, Termux, etc.) — tell the agent about the
+        # execution environment so it can translate paths and adapt behavior.
+        _env_hints = build_environment_hints()
+        if _env_hints:
+            prompt_parts.append(_env_hints)
+
         platform_key = (self.platform or "").lower().strip()
         if platform_key in PLATFORM_HINTS:
             prompt_parts.append(PLATFORM_HINTS[platform_key])

tests/agent/test_prompt_builder.py

@@ -18,6 +18,7 @@ from agent.prompt_builder import (
     build_skills_system_prompt,
     build_nous_subscription_prompt,
     build_context_files_prompt,
+    build_environment_hints,
     CONTEXT_FILE_MAX_CHARS,
     DEFAULT_AGENT_IDENTITY,
     TOOL_USE_ENFORCEMENT_GUIDANCE,
@@ -26,6 +27,7 @@ from agent.prompt_builder import (
     MEMORY_GUIDANCE,
     SESSION_SEARCH_GUIDANCE,
     PLATFORM_HINTS,
+    WSL_ENVIRONMENT_HINT,
 )
 from hermes_cli.nous_subscription import NousFeatureState, NousSubscriptionFeatures
 
@@ -770,6 +772,29 @@ class TestPromptBuilderConstants:
         assert "cli" in PLATFORM_HINTS
 
 
+# =========================================================================
+# Environment hints
+# =========================================================================
+
+class TestEnvironmentHints:
+    def test_wsl_hint_constant_mentions_mnt(self):
+        assert "/mnt/c/" in WSL_ENVIRONMENT_HINT
+        assert "WSL" in WSL_ENVIRONMENT_HINT
+
+    def test_build_environment_hints_on_wsl(self, monkeypatch):
+        import agent.prompt_builder as _pb
+        monkeypatch.setattr(_pb, "is_wsl", lambda: True)
+        result = _pb.build_environment_hints()
+        assert "/mnt/" in result
+        assert "WSL" in result
+
+    def test_build_environment_hints_not_wsl(self, monkeypatch):
+        import agent.prompt_builder as _pb
+        monkeypatch.setattr(_pb, "is_wsl", lambda: False)
+        result = _pb.build_environment_hints()
+        assert result == ""
+
+
 # =========================================================================
 # Conditional skill activation
 # =========================================================================