feat: add Dev and Preview title prefixes (#2464)

apps/backend/cmd/preview/sprite_ops.go

@@ -182,6 +182,7 @@ cd /app
 export KANDEV_HOME_DIR=/data
 export KANDEV_DOCKER_ENABLED=false
 export KANDEV_LOG_LEVEL=info
+export KANDEV_WEB_TITLE_PREFIX=Preview
 export KANDEV_WEB_DIST_DIR=/app/apps/web/dist
 # Preview mode: keep the mock agent while loading the built-in agent catalogue
 # so Settings can show agents that are available to install.

apps/backend/cmd/preview/sprite_ops_test.go

@@ -154,6 +154,9 @@ func TestBuildExtractScript(t *testing.T) {
 	if !strings.Contains(script, "KANDEV_WEB_DIST_DIR=/app/apps/web/dist") {
 		t.Errorf("expected KANDEV_WEB_DIST_DIR to point at packaged Vite dist")
 	}
+	if !strings.Contains(script, "KANDEV_WEB_TITLE_PREFIX=Preview") {
+		t.Errorf("expected preview title prefix in script")
+	}
 	if !strings.Contains(script, "ln -sf /app/apps/backend/bin/kandev      /usr/local/bin/kandev") {
 		t.Errorf("expected native kandev symlink in script")
 	}

apps/backend/internal/profiles/profiles.yaml

@@ -158,6 +158,15 @@ debug:
     dev:  "true"
     e2e:  ""
 
+# ── Browser identity ─────────────────────────────────────────────
+# Distinguish the local development tab from release and preview tabs without
+# changing the title of production or e2e environments.
+ui:
+  KANDEV_WEB_TITLE_PREFIX:
+    prod: ""
+    dev:  "Dev"
+    e2e:  ""
+
 # ── E2E test tuning ───────────────────────────────────────────────
 # Behaviour knobs that only matter when running playwright. These
 # don't belong in dev (would mask real interactions) and never in

apps/backend/internal/profiles/profiles_test.go

@@ -52,6 +52,9 @@ func TestApplyProfile_DefaultsToProd(t *testing.T) {
 			"false",
 		)
 	}
+	if _, ok := os.LookupEnv("KANDEV_WEB_TITLE_PREFIX"); ok {
+		t.Errorf("KANDEV_WEB_TITLE_PREFIX is set in prod; want it unset")
+	}
 }
 
 // TestApplyProfile_DevUsesDevelopmentDefaults verifies the mixed dev profile:
@@ -86,6 +89,23 @@ func TestApplyProfile_DevUsesDevelopmentDefaults(t *testing.T) {
 			"false",
 		)
 	}
+	if v := os.Getenv("KANDEV_WEB_TITLE_PREFIX"); v != "Dev" {
+		t.Errorf("KANDEV_WEB_TITLE_PREFIX = %q in dev; want %q", v, "Dev")
+	}
+}
+
+func TestApplyProfile_ExplicitTitlePrefixWinsInDev(t *testing.T) {
+	clearProfileSelectors(t)
+	clearProfilesYAMLVars(t)
+	t.Setenv("KANDEV_DEBUG_DEV_MODE", "true")
+	t.Setenv("KANDEV_WEB_TITLE_PREFIX", "Custom")
+
+	if _, _, err := ApplyProfile(); err != nil {
+		t.Fatalf("ApplyProfile: %v", err)
+	}
+	if v := os.Getenv("KANDEV_WEB_TITLE_PREFIX"); v != "Custom" {
+		t.Errorf("ApplyProfile overwrote explicit title prefix: got %q; want %q", v, "Custom")
+	}
 }
 
 // TestApplyProfile_E2EWinsOverDev checks the documented detection
@@ -118,6 +138,9 @@ func TestApplyProfile_E2EWinsOverDev(t *testing.T) {
 			"false",
 		)
 	}
+	if _, ok := os.LookupEnv("KANDEV_WEB_TITLE_PREFIX"); ok {
+		t.Errorf("KANDEV_WEB_TITLE_PREFIX is set in e2e; want it unset")
+	}
 }
 
 // TestApplyProfile_ExistingEnvWins is the precedence guarantee that
@@ -230,6 +253,7 @@ func TestProfilesYAML_ContainsRequiredSections(t *testing.T) {
 		"KANDEV_FEATURES_OFFICE:",
 		"KANDEV_FEATURES_APP_STATUS_BAR:",
 		"KANDEV_FEATURES_CLAUDE_BACKGROUND_PROMPT_HANDOFF:",
+		"KANDEV_WEB_TITLE_PREFIX:",
 	} {
 		if !strings.Contains(yaml, section) {
 			t.Errorf("embedded profiles.yaml missing section/key %q; embed broken or file truncated", section)

apps/cli/src/supervisor/manifest.test.ts

@@ -29,6 +29,7 @@ describe("supervisor launch manifest", () => {
         KANDEV_HOME_DIR: home,
         KANDEV_SERVER_PORT: "38429",
         KANDEV_DESKTOP_HEALTH_TOKEN: "health-token",
+        KANDEV_WEB_TITLE_PREFIX: "Preview",
         SECRET_TOKEN: "do-not-write",
       },
       home_dir: home,
@@ -45,6 +46,7 @@ describe("supervisor launch manifest", () => {
       KANDEV_HOME_DIR: home,
       KANDEV_SERVER_PORT: "38429",
       KANDEV_DESKTOP_HEALTH_TOKEN: "health-token",
+      KANDEV_WEB_TITLE_PREFIX: "Preview",
     });
     if (process.platform !== "win32") {
       expect((fs.statSync(target).mode & 0o777).toString(8)).toBe("600");
@@ -75,6 +77,7 @@ describe("supervisor launch manifest", () => {
         KANDEV_HOME_DIR: "/tmp/kandev",
         KANDEV_CONSOLE_LOG_LEVEL: "warn",
         KANDEV_DESKTOP_HEALTH_TOKEN: "health-token",
+        KANDEV_WEB_TITLE_PREFIX: "Dev",
         AWS_SECRET_ACCESS_KEY: "secret",
         GITHUB_TOKEN: "secret",
       }),
@@ -82,6 +85,7 @@ describe("supervisor launch manifest", () => {
       KANDEV_HOME_DIR: "/tmp/kandev",
       KANDEV_CONSOLE_LOG_LEVEL: "warn",
       KANDEV_DESKTOP_HEALTH_TOKEN: "health-token",
+      KANDEV_WEB_TITLE_PREFIX: "Dev",
     });
   });
 });

apps/cli/src/supervisor/manifest.ts

@@ -29,6 +29,7 @@ const ENV_ALLOWLIST = new Set([
   "KANDEV_AGENT_STANDALONE_PORT",
   "KANDEV_LOG_LEVEL",
   "KANDEV_CONSOLE_LOG_LEVEL",
+  "KANDEV_WEB_TITLE_PREFIX",
   "KANDEV_DEBUG_DEV_MODE",
   "KANDEV_DEBUG_AGENT_MESSAGES",
   "KANDEV_DEBUG_PPROF_ENABLED",

apps/web/e2e/fixtures/backend.ts

@@ -438,8 +438,9 @@ export const backendFixture = base.extend<object, { backend: BackendContext }>({
           // process.env.X before spawn — that already flows through the
           // `...sanitizeInheritedEnv(process.env)` spread above, and the
           // backend's ApplyProfile leaves already-set vars alone. (Note:
-          // KANDEV_FEATURES_* is the exception — it's stripped from the
-          // inherited env so the profile always governs feature flags.)
+          // KANDEV_FEATURES_* and KANDEV_WEB_TITLE_PREFIX are exceptions —
+          // they are stripped from the inherited env so the e2e profile
+          // always controls the baseline.)
           GIT_AUTHOR_NAME: "E2E Test",
           GIT_AUTHOR_EMAIL: "e2e@test.local",
           GIT_COMMITTER_NAME: "E2E Test",
@@ -539,6 +540,9 @@ function writeGitShimLauncher(shimDir: string, shimScript: string): void {
 //     in the test backend → /api/v1/office/* 404s. Dropping the whole
 //     KANDEV_FEATURES_* namespace lets the e2e profile govern feature flags so
 //     the suite always exercises them, regardless of where it's launched.
+//   - KANDEV_WEB_TITLE_PREFIX — the browser identity is profile-managed in
+//     this suite. Explicit per-test values are applied after this baseline is
+//     sanitized through `backend.restart(overrides)`.
 //   - PATH casing aliases — Windows commonly inherits `Path`; retaining it
 //     beside the fixture's new `PATH` makes child-process lookup order
 //     ambiguous. The caller restores one canonical PATH after sanitizing.
@@ -547,7 +551,9 @@ function sanitizeInheritedEnv(env: Record<string, string>): Record<string, strin
   delete cleaned.GH_TOKEN;
   delete cleaned.GITHUB_TOKEN;
   for (const key of Object.keys(cleaned)) {
-    if (key.startsWith("KANDEV_FEATURES_")) delete cleaned[key];
+    if (key === "KANDEV_WEB_TITLE_PREFIX" || key.startsWith("KANDEV_FEATURES_")) {
+      delete cleaned[key];
+    }
     if (key.toUpperCase() === "PATH") delete cleaned[key];
   }
   return cleaned;

apps/web/e2e/tests/system/title-prefix.spec.ts

@@ -0,0 +1,28 @@
+import { expect, test } from "../../fixtures/test-base";
+
+test.describe.serial("environment browser title prefixes", () => {
+  test("uses Dev for the development profile", async ({ backend, testPage }) => {
+    await backend.restart({ KANDEV_E2E_MOCK: "", KANDEV_DEBUG_DEV_MODE: "true" });
+
+    try {
+      await testPage.goto("/");
+      await expect(testPage).toHaveTitle("Dev Kandev");
+    } finally {
+      await backend.restart();
+    }
+  });
+
+  test("uses Preview for an explicitly configured preview backend", async ({
+    backend,
+    testPage,
+  }) => {
+    await backend.restart({ KANDEV_WEB_TITLE_PREFIX: "Preview" });
+
+    try {
+      await testPage.goto("/");
+      await expect(testPage).toHaveTitle("Preview Kandev");
+    } finally {
+      await backend.restart();
+    }
+  });
+});

docs/configuration.md

@@ -34,6 +34,10 @@ All env vars use the `KANDEV_` prefix. Nested keys map by replacing `.` with `_`
 
 The aliases on the right are explicit bindings - see `LoadWithPath` in `config.go` for the full list. New keys should follow the deterministic rule (`KANDEV_<SECTION>_<KEYUPPERCASE>`) unless there is a reason to add an alias.
 
+The `make dev` launcher uses `Dev` as the default browser title prefix, and PR
+preview environments use `Preview`. An explicit `KANDEV_WEB_TITLE_PREFIX`
+value overrides those environment defaults.
+
 ## Full `config.yaml` example
 
 Every key shown here has a default - copying the whole file changes nothing. Use it as a starting point and delete what you don't need to override.

docs/plans/dev-preview-title-prefixes/plan.md

@@ -0,0 +1,116 @@
+---
+spec: docs/specs/dev-preview-title-prefixes/spec.md
+created: 2026-08-09
+status: complete
+---
+
+# Implementation Plan: Environment-specific browser tab title prefixes
+
+## Overview
+
+Reuse the merged PR #2459 title-prefix contract and supply environment-specific
+defaults at the launch boundaries. The development profile will provide `Dev`,
+the PR preview startup script will provide `Preview`, and the CLI supervisor
+will preserve the prefix across restarts. Focused Go, CLI, browser, and docs
+checks will cover the launcher contracts and the visible browser result.
+
+## Backend and launchers
+
+### Development profile
+
+- `apps/backend/internal/profiles/profiles.yaml` (the target of the root
+  `profiles.yaml` symlink): add `KANDEV_WEB_TITLE_PREFIX` with an empty `prod`
+  and `e2e` value and `Dev` as the `dev` value.
+- `apps/backend/internal/profiles/profiles_test.go`: assert the dev profile
+  supplies `Dev` while the existing profile precedence remains intact.
+
+### PR preview launcher
+
+- `apps/backend/cmd/preview/sprite_ops.go`: export
+  `KANDEV_WEB_TITLE_PREFIX=Preview` in the generated preview startup script.
+- `apps/backend/cmd/preview/sprite_ops_test.go`: pin the generated script to
+  the `Preview` prefix alongside its existing startup assertions.
+
+### Supervisor environment contract
+
+- `apps/cli/src/supervisor/manifest.ts`: add `KANDEV_WEB_TITLE_PREFIX` to the
+  restart-manifest allowlist so any configured prefix survives a supervised
+  backend restart.
+- `apps/cli/src/supervisor/manifest.test.ts`: verify the title-prefix variable
+  is retained while arbitrary variables remain excluded.
+
+## Frontend and browser behavior
+
+No new frontend implementation is required. The existing PR #2459 path already
+renders the configured prefix in the server shell and applies it for the
+`/api/v1/app-state` boot path.
+
+Add `apps/web/e2e/tests/system/title-prefix.spec.ts` to restart the fixture
+backend with the development profile and with an explicit preview prefix, then
+assert both visible browser titles through the UI. The test restores the worker
+environment afterward.
+
+### Mobile parity contract
+
+The affected surface is browser metadata (`document.title`), not layout,
+navigation, touch input, scrolling, or viewport-bound UI. The desktop and
+mobile outcomes are identical, so no mobile-specific interaction test is
+needed; the E2E test and existing title helper contract cover the same
+viewport-independent behavior.
+
+## Public documentation
+
+- `docs/public/configuration.md`: explain that `make dev` defaults the title
+  prefix to `Dev` and PR previews use `Preview`, while explicit environment
+  values still override defaults.
+- `docs/configuration.md`: keep the internal configuration reference aligned.
+
+## Tests
+
+- **What:** the development profile resolves the title prefix to `Dev` and
+  leaves production/e2e defaults blank.
+  **File:** `apps/backend/internal/profiles/profiles_test.go`.
+  **How:** profile application unit test with isolated environment variables.
+- **What:** the preview startup script exports `Preview`.
+  **File:** `apps/backend/cmd/preview/sprite_ops_test.go`.
+  **How:** generated-script contract assertion.
+- **What:** the supervisor retains the title-prefix environment variable.
+  **File:** `apps/cli/src/supervisor/manifest.test.ts`.
+  **How:** allowlist unit test.
+- **What:** a configured runtime prefix is visible in the browser title.
+  **File:** `apps/web/e2e/tests/system/title-prefix.spec.ts`.
+  **How:** worker backend restart plus Playwright UI assertion.
+
+## E2E Tests
+
+- **Scenarios:** GIVEN a fixture backend restarted with the development profile,
+  WHEN the browser opens Kandev, THEN the page title is `Dev Kandev`; GIVEN a
+  fixture backend restarted with `KANDEV_WEB_TITLE_PREFIX=Preview`, THEN the
+  page title is `Preview Kandev`.
+- **File:** `apps/web/e2e/tests/system/title-prefix.spec.ts`.
+- **What to verify:** the user-visible browser tab title after a fresh page
+  navigation.
+
+## Verification Results
+
+- `cd apps/backend && go test -tags fts5 ./internal/profiles ./cmd/preview` —
+  passed, 30 tests in 2 packages.
+- `cd apps && pnpm --filter kandev test -- --run src/dev.test.ts src/supervisor/manifest.test.ts` —
+  passed, 2 files and 6 tests.
+- `cd apps/web && pnpm e2e:run --project chromium tests/system/title-prefix.spec.ts` —
+  passed, 2 Playwright tests (`Dev Kandev` and `Preview Kandev`).
+- `node --test scripts/validate-public-docs.test.mjs` — passed, 58 tests.
+- `node scripts/validate-public-docs.mjs` — passed, 41 published pages.
+- `pnpm exec prettier --check ...` — passed for the changed TypeScript files.
+- `git diff --check` — passed.
+
+## Implementation Waves And Parallel Candidates
+
+Wave 1 (sequential; the launch contracts and their tests are one cohesive
+change):
+
+- [x] [task-01-launch-prefixes](task-01-launch-prefixes.md)
+
+## Open Questions
+
+None.

docs/plans/dev-preview-title-prefixes/task-01-launch-prefixes.md

@@ -0,0 +1,104 @@
+---
+id: "01-launch-prefixes"
+title: "Set environment title prefixes"
+status: done
+wave: 1
+depends_on: []
+plan: "plan.md"
+spec: "../../specs/dev-preview-title-prefixes/spec.md"
+---
+
+# Task 01: Set environment title prefixes
+
+## Acceptance
+
+- `make dev` selects a backend profile that produces `Dev Kandev` by default,
+  while normal production/start and e2e profiles remain unprefixed unless an
+  explicit environment override is supplied.
+- PR preview startup produces `Preview Kandev`, and the CLI supervisor retains
+  `KANDEV_WEB_TITLE_PREFIX` when it writes and reuses its restart manifest.
+- Focused browser, Go, TypeScript, and public-doc checks pass for the new
+  launcher behavior.
+
+## Verification
+
+Run the focused unit checks:
+
+```bash
+cd apps/backend && go test -tags fts5 ./internal/profiles ./cmd/preview
+cd ../ && pnpm --filter kandev test -- --run src/dev.test.ts src/supervisor/manifest.test.ts
+```
+
+Run the browser contract against the managed production E2E build:
+
+```bash
+cd apps/web && pnpm e2e:run --project chromium tests/system/title-prefix.spec.ts
+```
+
+Validate public documentation:
+
+```bash
+node --test scripts/validate-public-docs.test.mjs
+node scripts/validate-public-docs.mjs
+```
+
+On a fresh worktree, install workspace dependencies first with
+`cd apps && pnpm install --frozen-lockfile`.
+
+## Files likely touched
+
+- `apps/backend/internal/profiles/profiles.yaml`
+- `apps/backend/internal/profiles/profiles_test.go`
+- `apps/backend/cmd/preview/sprite_ops.go`
+- `apps/backend/cmd/preview/sprite_ops_test.go`
+- `apps/cli/src/supervisor/manifest.ts`
+- `apps/cli/src/supervisor/manifest.test.ts`
+- `apps/web/e2e/tests/system/title-prefix.spec.ts`
+- `docs/configuration.md`
+- `docs/public/configuration.md`
+
+## Dependencies
+
+None.
+
+## Parallelism
+
+Sequential. The profile, preview script, supervisor allowlist, and browser test
+all implement one environment-to-title contract, and the tests share the same
+behavioral acceptance criteria.
+
+## Inputs
+
+- `docs/specs/dev-preview-title-prefixes/spec.md`
+- `docs/plans/dev-preview-title-prefixes/plan.md`
+- The merged PR #2459 `KANDEV_WEB_TITLE_PREFIX` contract.
+- Existing profile precedence: explicit shell/launcher environment overrides
+  profile defaults.
+- Existing backend and web E2E fixtures.
+
+## Output contract
+
+Report the changed files, exact test commands and results, any E2E cleanup, and
+whether the task and plan statuses were updated. Record blockers and remaining
+risks explicitly.
+
+## Results
+
+Implemented the profile, preview launcher, and supervisor environment
+contracts. Added browser coverage for both environment defaults and updated the
+public and internal configuration references.
+
+Verification completed:
+
+- `cd apps/backend && go test -tags fts5 ./internal/profiles ./cmd/preview` —
+  passed, 30 tests in 2 packages.
+- `cd apps && pnpm --filter kandev test -- --run src/dev.test.ts src/supervisor/manifest.test.ts` —
+  passed, 2 files and 6 tests.
+- `cd apps/web && pnpm e2e:run --project chromium tests/system/title-prefix.spec.ts` —
+  passed, 2 Playwright tests.
+- `node --test scripts/validate-public-docs.test.mjs` — passed, 58 tests.
+- `node scripts/validate-public-docs.mjs` — passed, 41 published pages.
+- `pnpm exec prettier --check ...` and `git diff --check` — passed.
+
+The managed E2E runner restored the fixture backend after each test; no
+generated files are tracked in the worktree.

docs/public/configuration.md

@@ -58,7 +58,7 @@ Some common camelCase keys have explicit compatibility aliases. Use the document
 | `server.readTimeout` | `KANDEV_SERVER_READTIMEOUT` | `30` | HTTP read timeout in seconds. |
 | `server.writeTimeout` | `KANDEV_SERVER_WRITETIMEOUT` | `30` | HTTP write timeout in seconds. |
 | `server.webInternalUrl` | `KANDEV_WEB_INTERNAL_URL` | empty | Development reverse-proxy target for a separately running web app. Installed releases normally serve embedded assets. |
-| `server.webTitlePrefix` | `KANDEV_WEB_TITLE_PREFIX` | empty | Prefixes the browser tab title as `<prefix> Kandev` (for example `TEST` renders `TEST Kandev`), so several instances stay distinguishable in adjacent tabs. Empty keeps the plain `Kandev` title. |
+| `server.webTitlePrefix` | `KANDEV_WEB_TITLE_PREFIX` | empty | Prefixes the browser tab title as `<prefix> Kandev` (for example `TEST` renders `TEST Kandev`), so several instances stay distinguishable in adjacent tabs. `make dev` defaults to `Dev`; PR previews use `Preview`. An explicit value overrides these defaults. Empty keeps the plain `Kandev` title. |
 
 The default host exposes the server on every interface even though the CLI prints a `localhost` URL. The current local product path must not be treated as an authenticated multi-user perimeter. For remote access, bind to loopback and use a trusted authenticated tunnel/proxy, or isolate the network at the deployment layer.
 

docs/specs/dev-preview-title-prefixes/spec.md

@@ -0,0 +1,84 @@
+---
+status: shipped
+created: 2026-08-09
+owner: Kandev
+---
+
+# Environment-specific browser tab title prefixes
+
+## Why
+
+Developers often keep a local development instance and one or more pull-request
+preview instances open at the same time. Identical `Kandev` browser tabs make it
+easy to use the wrong instance.
+
+## What
+
+- A Kandev browser tab title uses the existing `<prefix> Kandev` composition.
+- A backend started in the development profile, including `make dev`, uses the
+  default prefix `Dev`, so its tab title is `Dev Kandev`.
+- A PR preview environment uses the prefix `Preview`, so its tab title is
+  `Preview Kandev`.
+- An explicitly supplied `KANDEV_WEB_TITLE_PREFIX` continues to take precedence
+  over a profile default. Its value is trimmed by the existing title-prefix
+  contract.
+- A normal production/start launch with no explicit prefix keeps the plain
+  `Kandev` title.
+- The prefix is present both on the initial server-rendered page and after a
+  client boot from `/api/v1/app-state`, using the title behavior delivered by
+  PR #2459.
+- A supervised backend restart keeps the configured prefix.
+
+## API surface
+
+The existing environment contract remains the public configuration surface:
+
+| Environment | `KANDEV_WEB_TITLE_PREFIX` | Result |
+|---|---|---|
+| Development profile (`make dev`) | `Dev` by default | `Dev Kandev` |
+| PR preview launcher | `Preview` | `Preview Kandev` |
+| Normal start with no override | unset | `Kandev` |
+| Any launch with an explicit override | caller value | `<value> Kandev` |
+
+The prefix is process configuration. It is not stored in the database and is
+not changed from the Kandev UI.
+
+## Failure modes
+
+- If the prefix is unset or blank, the title remains `Kandev`.
+- If the preview launcher cannot set the environment variable, the preview
+  falls back to the existing plain-title behavior rather than failing startup.
+- If a supervised restart occurs, the launcher preserves the allowlisted prefix
+  in the restart manifest so the restarted backend does not silently change its
+  title.
+
+## Persistence guarantees
+
+The title prefix lasts for the lifetime of the launched environment and its
+supervised restarts. It is not persisted across separate launches unless the
+caller supplies the same environment or profile again.
+
+## Scenarios
+
+- **GIVEN** a clean checkout with no title-prefix override, **WHEN** the user
+  runs `make dev` and opens the Kandev URL, **THEN** the browser title is
+  `Dev Kandev`.
+- **GIVEN** a PR preview deployment, **WHEN** its startup service launches
+  Kandev, **THEN** the browser title is `Preview Kandev`.
+- **GIVEN** a development profile and `KANDEV_WEB_TITLE_PREFIX=Custom`, **WHEN**
+  the backend starts, **THEN** the browser title is `Custom Kandev`.
+- **GIVEN** a normal start with no title-prefix environment variable, **WHEN**
+  the user opens Kandev, **THEN** the browser title is `Kandev`.
+- **GIVEN** a preview or development backend with a configured prefix, **WHEN**
+  its supervisor restarts the backend, **THEN** the browser title retains the
+  same prefix.
+- **GIVEN** a phone-sized browser viewport, **WHEN** either environment is
+  opened, **THEN** the same title is shown; no viewport-specific interaction is
+  required.
+
+## Out of scope
+
+- Changing the title dynamically from the Kandev UI.
+- Changing desktop window titles, CLI output, logs, or task titles.
+- Automatically labeling arbitrary self-hosted instances beyond the existing
+  explicit environment variable.