fix(daemon): add Nix Home Manager PATH support

Add Nix Home Manager profile bin directories to generated gateway service PATHs on macOS and Linux.

Includes ~/.nix-profile/bin fallback when NIX_PROFILES is absent, honors NIX_PROFILES right-to-left precedence when present, and covers the service PATH resolver with focused unit tests.

Closes #44402.

src/daemon/service-env.test.ts

@@ -172,6 +172,102 @@ describe("getMinimalServicePathParts - Linux user directories", () => {
   });
 });
 
+describe("getMinimalServicePathParts - Nix Home Manager", () => {
+  it("falls back to default Nix profile when NIX_PROFILES is absent on Linux", () => {
+    const result = getMinimalServicePathParts({
+      platform: "linux",
+      home: "/home/testuser",
+    });
+
+    expect(result).toContain("/home/testuser/.nix-profile/bin");
+  });
+
+  it("falls back to default Nix profile when NIX_PROFILES is absent on macOS", () => {
+    const result = getMinimalServicePathParts({
+      platform: "darwin",
+      home: "/Users/testuser",
+    });
+
+    expect(result).toContain("/Users/testuser/.nix-profile/bin");
+  });
+
+  it("places rightmost NIX_PROFILES entry before leftmost on Linux", () => {
+    const result = getMinimalServicePathPartsFromEnv({
+      platform: "linux",
+      env: {
+        HOME: "/home/testuser",
+        NIX_PROFILES: "/nix/var/nix/profiles/default /home/testuser/.nix-profile",
+      },
+    });
+
+    const userIdx = result.indexOf("/home/testuser/.nix-profile/bin");
+    const defaultIdx = result.indexOf("/nix/var/nix/profiles/default/bin");
+    expect(userIdx).toBeGreaterThan(-1);
+    expect(defaultIdx).toBeGreaterThan(-1);
+    expect(userIdx).toBeLessThan(defaultIdx);
+  });
+
+  it("places rightmost NIX_PROFILES entry before leftmost on macOS", () => {
+    const result = getMinimalServicePathPartsFromEnv({
+      platform: "darwin",
+      env: {
+        HOME: "/Users/testuser",
+        NIX_PROFILES: "/nix/var/nix/profiles/default /Users/testuser/.nix-profile",
+      },
+    });
+
+    const userIdx = result.indexOf("/Users/testuser/.nix-profile/bin");
+    const defaultIdx = result.indexOf("/nix/var/nix/profiles/default/bin");
+    expect(userIdx).toBeGreaterThan(-1);
+    expect(defaultIdx).toBeGreaterThan(-1);
+    expect(userIdx).toBeLessThan(defaultIdx);
+  });
+
+  it("includes single Nix profile from NIX_PROFILES on Linux", () => {
+    const result = getMinimalServicePathPartsFromEnv({
+      platform: "linux",
+      env: {
+        HOME: "/home/testuser",
+        NIX_PROFILES: "/nix/var/nix/profiles/per-user/testuser/profile",
+      },
+    });
+
+    expect(result).toContain("/nix/var/nix/profiles/per-user/testuser/profile/bin");
+  });
+
+  it("includes single Nix profile from NIX_PROFILES on macOS", () => {
+    const result = getMinimalServicePathPartsFromEnv({
+      platform: "darwin",
+      env: {
+        HOME: "/Users/testuser",
+        NIX_PROFILES: "/nix/var/nix/profiles/per-user/testuser/profile",
+      },
+    });
+
+    expect(result).toContain("/nix/var/nix/profiles/per-user/testuser/profile/bin");
+  });
+
+  it("preserves Nix precedence across three profiles", () => {
+    const result = getMinimalServicePathPartsFromEnv({
+      platform: "linux",
+      env: {
+        HOME: "/home/testuser",
+        NIX_PROFILES:
+          "/nix/var/nix/profiles/default /nix/var/nix/profiles/per-user/testuser/custom /home/testuser/.nix-profile",
+      },
+    });
+
+    const userIdx = result.indexOf("/home/testuser/.nix-profile/bin");
+    const customIdx = result.indexOf("/nix/var/nix/profiles/per-user/testuser/custom/bin");
+    const defaultIdx = result.indexOf("/nix/var/nix/profiles/default/bin");
+    expect(userIdx).toBeGreaterThan(-1);
+    expect(customIdx).toBeGreaterThan(-1);
+    expect(defaultIdx).toBeGreaterThan(-1);
+    expect(userIdx).toBeLessThan(customIdx);
+    expect(customIdx).toBeLessThan(defaultIdx);
+  });
+});
+
 describe("buildMinimalServicePath", () => {
   const splitPath = (value: string, platform: NodeJS.Platform) =>
     value.split(platform === "win32" ? path.win32.delimiter : path.posix.delimiter);

src/daemon/service-env.ts

@@ -106,6 +106,23 @@ function addCommonEnvConfiguredBinDirs(
   addNonEmptyDir(dirs, appendSubdir(env?.ASDF_DATA_DIR, "shims"));
 }
 
+// Nix shell precedence: rightmost profile in NIX_PROFILES = highest priority.
+// When NIX_PROFILES is absent, fall back to the default single-user profile.
+function addNixProfileBinDirs(
+  dirs: string[],
+  home: string,
+  env: Record<string, string | undefined> | undefined,
+): void {
+  const nixProfiles = env?.NIX_PROFILES?.trim();
+  if (nixProfiles) {
+    for (const profile of nixProfiles.split(/\s+/).toReversed()) {
+      addNonEmptyDir(dirs, appendSubdir(profile, "bin"));
+    }
+  } else {
+    dirs.push(`${home}/.nix-profile/bin`);
+  }
+}
+
 function resolveSystemPathDirs(platform: NodeJS.Platform): string[] {
   if (platform === "darwin") {
     return ["/opt/homebrew/bin", "/usr/local/bin", "/usr/bin", "/bin"];
@@ -148,6 +165,9 @@ export function resolveDarwinUserBinDirs(
   // Common user bin directories
   addCommonUserBinDirs(dirs, home);
 
+  // Nix Home Manager (cross-platform)
+  addNixProfileBinDirs(dirs, home, env);
+
   // Node version managers - macOS specific paths
   // nvm: no stable default path, depends on user's shell configuration
   // fnm: macOS default is ~/Library/Application Support/fnm, not ~/.fnm
@@ -182,6 +202,9 @@ export function resolveLinuxUserBinDirs(
   // Common user bin directories
   addCommonUserBinDirs(dirs, home);
 
+  // Nix Home Manager (cross-platform)
+  addNixProfileBinDirs(dirs, home, env);
+
   // Node version managers
   dirs.push(`${home}/.nvm/current/bin`); // nvm with current symlink
   dirs.push(`${home}/.fnm/current/bin`); // fnm