agent: dev launcher — own Linux env-var contract, add dev:tauri, doc sweep

The 2026-05-12 engine-slop pass removed runtime std::env::set_var mutation from src-tauri/src/lib.rs and replaced it with warn_if_x11_env_unset_on_wayland. With no launcher owning the contract, Linux Wayland dogfood was about to regress.

run.sh:
- now owns Linux launcher env defaults via case "$(uname -s)"
  LIBCLANG_PATH=/usr/lib64/llvm21/lib64 (user-set wins)
  WEBKIT_DISABLE_DMABUF_RENDERER=1 (always on Linux; user-set wins)
  GDK_BACKEND=x11, WINIT_UNIX_BACKEND=x11 (Wayland only; user-set wins)
- 60s Vite readiness timeout
- detects early Vite exit (kill -0 + wait) instead of hanging forever
- trap installed before wait so Ctrl-C cleans up
- args forwarded: ./run.sh --release etc.
- non-exec final Tauri launch preserved so cleanup trap fires

package.json:
- "dev:tauri": "./run.sh" — canonical discoverable dev command

Docs:
- README, dev-setup, architecture-map runtime + launcher pages updated with the new contract; canonical command is npm run dev:tauri (./run.sh as direct equivalent)
- dev-launcher-and-scripts.md replaces the incorrect "kills process group" claim with honest "kills the spawned npm process"
- dev-setup.md path /CORBEL-Projects/magnotia → /CORBEL-Projects/transcription-app
- gpu-tuning/plan.md gets a superseded note rather than rewriting the original rationale
- engine-slop-residuals.md gains Area F (packaged-binary launcher contract) with honest wrapper-vs-.desktop trade-off documented

Verification: bash -n run.sh; shellcheck clean; cargo check -p magnotia green; npm pkg get 'scripts.dev:tauri' returns "./run.sh"; stale-ref sweep clean across living docs.

docs/architecture-map/02-tauri-runtime/README.md

@@ -2,7 +2,7 @@
 name: Slice 02 — Tauri runtime
 type: architecture-map-page
 slice: 02-tauri-runtime
-last_verified: 2026/05/09
+last_verified: 2026/05/12
 ---
 
 # Slice 02 — Tauri runtime
@@ -29,7 +29,7 @@ last_verified: 2026/05/09
 
 App boot, config, tests:
 
-- [App lifecycle](app-lifecycle.md). `src-tauri/src/main.rs` and `src-tauri/src/lib.rs`. Run entry, AppState construction, plugin wiring, preferences injection, X11-on-Wayland workaround, panic hook, error-log pruning, command registration.
+- [App lifecycle](app-lifecycle.md). `src-tauri/src/main.rs` and `src-tauri/src/lib.rs`. Run entry, AppState construction, plugin wiring, preferences injection, Linux launcher-env warning, panic hook, error-log pruning, command registration.
 - [System tray](system-tray.md). Desktop-only tray icon and menu (`src-tauri/src/tray.rs`).
 - [Tauri config](tauri-config.md). `tauri.conf.json` plus the Linux native-decorations overlay; CSP, window defaults, bundle settings.
 - [Capabilities and ACL](capabilities-and-acl.md). The two ACL files in `capabilities/`, what each scopes, and the Phase 9 high-risk-permission firewall.
@@ -57,7 +57,7 @@ Individual command pages (linked from the commands index):
 - `commands::update::install_update` returns a hard-coded "Updates are disabled until release signing is configured." (`src-tauri/src/commands/update.rs:15`). The integration test `updater_is_signed_or_absent` (`src-tauri/tests/config_hardening.rs:35`) only asserts that *if* an updater config ships, it carries a non-empty pubkey. There is currently no updater config in `tauri.conf.json`, so the test is an empty no-op.
 - `commands::power::PowerAssertion` is a no-op on Linux and Windows (`src-tauri/src/commands/power.rs:90`). Only macOS has a real implementation via `objc2`. The doc comment promises `SetThreadExecutionState` (Windows) and logind inhibitors (Linux), but neither is wired up. Symptom: long live-dictation sessions on Linux can be idled by the compositor.
 - `src-tauri/.cargo/config.toml` hard-codes `LIBCLANG_PATH = "C:\\Program Files\\LLVM\\bin"` (Windows). It is harmless on non-Windows hosts (env var is just unused) but it is a foot-gun if someone moves Clang elsewhere on Windows. See [Cargo and features](cargo-and-features.md).
-- The Linux Wayland workaround in `lib.rs` (`ensure_x11_on_wayland`) sets env vars before any threads spawn. This is the right pattern, but it ships even when the user is on a working DMA-BUF stack. The override knob is `WEBKIT_DISABLE_DMABUF_RENDERER=0` set by the user; documented in the function header but not surfaced anywhere user-visible.
+- The Linux rendering workaround in `lib.rs` (`warn_if_x11_env_unset_on_wayland`) now warns when the launcher has not set the expected env vars; it no longer mutates the process environment. In development, `run.sh` / `npm run dev:tauri` owns the defaults (`WEBKIT_DISABLE_DMABUF_RENDERER=1` on Linux; `GDK_BACKEND=x11` and `WINIT_UNIX_BACKEND=x11` on Wayland). The user opt-out remains `WEBKIT_DISABLE_DMABUF_RENDERER=0`, set before launching.
 - `commands::diagnostics::install_panic_hook` writes a "minimal text dump" without backtraces unless the user has `RUST_BACKTRACE=1` set (`src-tauri/src/commands/diagnostics.rs:42`). The packaged binary does not set it, so production crash dumps will lack stack traces. Document or default-enable.
 - `commands::audio::list_audio_devices` is gated `ensure_main_window` but the `secondary-windows` capability does not invoke it, which is correct. The `clipboard::copy_to_clipboard` command, by contrast, has no main-window guard and any window with the `core:default` permission can call it; intentional, but worth flagging.