feat(config): add SKILLC_HOME environment variable override

Per [[RFC-0009:C-ENV-OVERRIDE]], adds SKILLC_HOME env var to override
home directory detection for all global paths. This enables:

- Cross-platform test isolation (HOME only works on Unix)
- Custom installation locations
- Portable/relocatable installations

Also fixes MCP skc_lint and skc_build to use resolve_skill() instead
of global_source_store(), enabling project-local skill resolution.

Test changes:
- All integration tests now automatically isolated via SKILLC_HOME
- Removed with_mock_home() - mock home is always created
- Unified run_skc() always sets SKILLC_HOME
- Removed cfg(unix) from 16 tests - now cross-platform
- MCP tests use spawn_with_context() for consistent isolation

Author: lucifer1004

CHANGELOG.md

@@ -7,6 +7,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.1.1] - 2026-01-31
+
+### Added
+
+- `SKILLC_HOME` env var overrides home directory detection (WI-2026-01-31-001)
+
+### Fixed
+
+- MCP lint/build use resolve_skill() (WI-2026-01-31-002)
+
 ## [0.1.0] - 2026-01-30
 
 ### Added

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "skillc"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2024"
 license = "MIT OR Apache-2.0"
 description = "A development kit for Agent Skills - the open format for extending AI agent capabilities"
@@ -70,4 +70,5 @@ assert_cmd = "2"
 filetime = "0.2"
 insta = { version = "1", features = ["json"] }
 predicates = "3"
+temp-env = "0.3"
 tempfile = "3"

Cargo.toml

@@ -1,9 +1,9 @@
 <!-- GENERATED: do not edit. Source: RFC-0009 -->
-<!-- SIGNATURE: sha256:afbd12b3a17ce6d4c52fd6434461004ac091b259e824151cc4698a43fdb828d0 -->
+<!-- SIGNATURE: sha256:e1e5f61c6203e7687beabd4d56b4d497a29cd181816aacd597a1411b458f2f6f -->
 
 # RFC-0009: Configuration
 
-> **Version:** 0.1.0 | **Status:** normative | **Phase:** test
+> **Version:** 0.2.0 | **Status:** normative | **Phase:** test
 
 ---
 
@@ -137,10 +137,33 @@ Changing the tokenizer setting invalidates existing search indexes. The search c
 
 *Since: v0.1.0*
 
+### [RFC-0009:C-ENV-OVERRIDE] Environment Variable Override (Normative) <a id="rfc-0009c-env-override"></a>
+
+The `SKILLC_HOME` environment variable, if set, MUST override the default home directory detection for all global paths.
+
+When `SKILLC_HOME` is set to a path (e.g., `/custom/home`):
+- `global_skillc_dir()` MUST return `$SKILLC_HOME/.skillc/` (e.g., `/custom/home/.skillc/`)
+- All derived paths (global source store, global runtime, etc.) MUST use this base
+- `find_project_root()` MUST exclude `$SKILLC_HOME` from project root detection
+
+When `SKILLC_HOME` is not set:
+- The implementation MUST fall back to `dirs::home_dir()` behavior
+
+**Rationale:** This enables:
+1. Cross-platform test isolation (HOME env var only works on Unix)
+2. Custom installation locations
+3. Portable/relocatable installations
+
+*Since: v0.2.0*
+
 ---
 
 ## Changelog
 
+### v0.2.0 (2026-01-31)
+
+Add SKILLC_HOME override
+
 ### v0.1.0 (2026-01-30)
 
 Initial release

docs/rfc/RFC-0009.md

@@ -1,3 +1,11 @@
+[[releases]]
+version = "0.1.1"
+date = "2026-01-31"
+refs = [
+    "WI-2026-01-31-001",
+    "WI-2026-01-31-002",
+]
+
 [[releases]]
 version = "0.1.0"
 date = "2026-01-30"

gov/releases.toml

@@ -0,0 +1,8 @@
+{
+  "clause_id": "C-ENV-OVERRIDE",
+  "title": "Environment Variable Override",
+  "kind": "normative",
+  "status": "active",
+  "text": "The `SKILLC_HOME` environment variable, if set, MUST override the default home directory detection for all global paths.\n\nWhen `SKILLC_HOME` is set to a path (e.g., `/custom/home`):\n- `global_skillc_dir()` MUST return `$SKILLC_HOME/.skillc/` (e.g., `/custom/home/.skillc/`)\n- All derived paths (global source store, global runtime, etc.) MUST use this base\n- `find_project_root()` MUST exclude `$SKILLC_HOME` from project root detection\n\nWhen `SKILLC_HOME` is not set:\n- The implementation MUST fall back to `dirs::home_dir()` behavior\n\n**Rationale:** This enables:\n1. Cross-platform test isolation (HOME env var only works on Unix)\n2. Custom installation locations\n3. Portable/relocatable installations",
+  "since": "0.2.0"
+}

gov/rfc/RFC-0009/clauses/C-ENV-OVERRIDE.json

@@ -1,12 +1,12 @@
 {
   "rfc_id": "RFC-0009",
   "title": "Configuration",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "status": "normative",
   "phase": "test",
   "owners": ["@govctl-org"],
   "created": "2026-01-30",
-  "updated": "2026-01-30",
+  "updated": "2026-01-31",
   "sections": [
     {
       "title": "Summary",
@@ -17,15 +17,22 @@
       "clauses": [
         "clauses/C-FILES.json",
         "clauses/C-RESOLUTION.json",
-        "clauses/C-TOKENIZER.json"
+        "clauses/C-TOKENIZER.json",
+        "clauses/C-ENV-OVERRIDE.json"
       ]
     }
   ],
   "changelog": [
+    {
+      "version": "0.2.0",
+      "date": "2026-01-31",
+      "notes": "Add SKILLC_HOME override"
+    },
     {
       "version": "0.1.0",
       "date": "2026-01-30",
       "notes": "Initial release"
     }
-  ]
+  ],
+  "signature": "e1e5f61c6203e7687beabd4d56b4d497a29cd181816aacd597a1411b458f2f6f"
 }

gov/rfc/RFC-0009/rfc.json

@@ -0,0 +1,32 @@
+[govctl]
+schema = 1
+id = "WI-2026-01-31-001"
+title = "Add SKILLC_HOME environment variable override"
+status = "done"
+created = "2026-01-31"
+started = "2026-01-31"
+completed = "2026-01-31"
+refs = ["RFC-0009"]
+
+[content]
+description = "Add `SKILLC_HOME` environment variable to override home directory detection, enabling cross-platform test isolation and custom installation locations."
+
+[[content.acceptance_criteria]]
+text = "`SKILLC_HOME` env var overrides home directory detection"
+status = "done"
+category = "added"
+
+[[content.acceptance_criteria]]
+text = "Cross-platform test isolation using `SKILLC_HOME`"
+status = "done"
+category = "chore"
+
+[[content.acceptance_criteria]]
+text = "All `cfg(unix)` tests become cross-platform"
+status = "done"
+category = "chore"
+
+[[content.acceptance_criteria]]
+text = "All tests pass"
+status = "done"
+category = "chore"

gov/work/2026-01-31-add-skillc-home-environment-variable-override.toml

@@ -0,0 +1,26 @@
+[govctl]
+schema = 1
+id = "WI-2026-01-31-002"
+title = "fix(mcp): use resolve_skill for lint and build tools"
+status = "done"
+created = "2026-01-31"
+started = "2026-01-31"
+completed = "2026-01-31"
+
+[content]
+description = "Fix MCP skc_lint and skc_build to use resolve_skill() instead of global_source_store(), enabling project-local skill resolution. Refactor MCP tests to use spawn_with_context() for consistent isolation."
+
+[[content.acceptance_criteria]]
+text = "MCP lint/build use resolve_skill()"
+status = "done"
+category = "fixed"
+
+[[content.acceptance_criteria]]
+text = "MCP tests use spawn_with_context()"
+status = "done"
+category = "chore"
+
+[[content.acceptance_criteria]]
+text = "All tests pass"
+status = "done"
+category = "chore"

gov/work/2026-01-31-fix-mcp-use-resolve-skill-for-lint-and-build-tools.toml

@@ -280,10 +280,19 @@ pub fn get_tokenizer() -> Tokenizer {
     Tokenizer::default()
 }
 
-/// Get the global skillc directory (~/.skillc/)
+/// Get the global skillc directory.
+///
+/// Per [[RFC-0009:C-ENV-OVERRIDE]], checks `SKILLC_HOME` first, then falls back to `~/.skillc/`.
+/// When `SKILLC_HOME` is set, it acts as the home directory override, so `.skillc` is appended.
 ///
 /// Returns error if home directory cannot be determined.
 pub fn global_skillc_dir() -> Result<PathBuf> {
+    // Check SKILLC_HOME override first (enables cross-platform test isolation)
+    // SKILLC_HOME acts as home directory override, so we append .skillc
+    if let Ok(skillc_home) = env::var("SKILLC_HOME") {
+        return Ok(PathBuf::from(skillc_home).join(".skillc"));
+    }
+
     let home = dirs::home_dir()
         .ok_or_else(|| SkillcError::Internal("could not determine home directory".to_string()))?;
     Ok(home.join(".skillc"))
@@ -297,14 +306,21 @@ pub fn global_source_store() -> Result<PathBuf> {
 /// Find project root by walking up from CWD, looking for `.skillc/` directory.
 ///
 /// Returns the project root directory (containing `.skillc/`) if found.
-/// Note: The home directory is excluded - `~/.skillc/` is the global store, not a project.
+/// Note: The home directory (or SKILLC_HOME) is excluded - its `.skillc/` is the global store, not a project.
 pub fn find_project_root() -> Option<PathBuf> {
-    let home = dirs::home_dir();
+    // Get the home directory to exclude from project root search
+    // If SKILLC_HOME is set, use that; otherwise use the real home
+    let excluded_home = if let Ok(skillc_home) = env::var("SKILLC_HOME") {
+        Some(PathBuf::from(skillc_home))
+    } else {
+        dirs::home_dir()
+    };
+
     let mut dir = env::current_dir().ok()?;
 
     loop {
-        // Don't treat home directory as project root (that's the global store)
-        if Some(&dir) != home.as_ref() && dir.join(".skillc").is_dir() {
+        // Don't treat home directory as project root (its .skillc is the global store)
+        if Some(&dir) != excluded_home.as_ref() && dir.join(".skillc").is_dir() {
             return Some(dir);
         }
         if !dir.pop() {