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- gpu-tuning/plan.md gets a superseded note rather than rewriting the original rationale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.

run.sh

@@ -1,22 +1,51 @@
 #!/usr/bin/env bash
 # Magnotia dev launcher. Starts Vite first, waits for it to bind port 1420,
 # then runs Tauri without triggering a second Vite instance.
+# Sets the Linux rendering env vars that warn_if_x11_env_unset_on_wayland
+# (src-tauri/src/lib.rs) expects the launcher to own.
 # For performance testing use: npm run tauri build
 set -euo pipefail
 cd "$(dirname "$0")"
 
-export LIBCLANG_PATH=/usr/lib64/llvm21/lib64
+case "$(uname -s)" in
+    Linux)
+        # Bindgen libclang path. Fedora 41/LLVM 21 default; user-set wins.
+        export LIBCLANG_PATH="${LIBCLANG_PATH:-/usr/lib64/llvm21/lib64}"
+        # iGPU idle-cost workaround. Set to 0 explicitly to opt out.
+        export WEBKIT_DISABLE_DMABUF_RENDERER="${WEBKIT_DISABLE_DMABUF_RENDERER:-1}"
+        if [ "${XDG_SESSION_TYPE:-}" = "wayland" ]; then
+            export GDK_BACKEND="${GDK_BACKEND:-x11}"
+            export WINIT_UNIX_BACKEND="${WINIT_UNIX_BACKEND:-x11}"
+        fi
+        ;;
+esac
 
 printf 'Starting Vite dev server...\n' >&2
 npm run dev:frontend &
 VITE_PID=$!
 
-until curl -sf http://localhost:1420 > /dev/null 2>&1; do sleep 0.5; done
-printf 'Vite ready. Launching Tauri...\n' >&2
-
 cleanup() {
     kill "$VITE_PID" 2>/dev/null || true
 }
 trap cleanup EXIT INT TERM
 
-npx tauri dev --config '{"build":{"beforeDevCommand":""}}'
+# Wait up to 60s for Vite, bailing if it exits early.
+for _ in $(seq 1 120); do
+    if curl -sf http://localhost:1420 > /dev/null 2>&1; then
+        break
+    fi
+    if ! kill -0 "$VITE_PID" 2>/dev/null; then
+        printf 'Vite dev server exited before becoming ready.\n' >&2
+        wait "$VITE_PID"
+        exit 1
+    fi
+    sleep 0.5
+done
+
+if ! curl -sf http://localhost:1420 > /dev/null 2>&1; then
+    printf 'Timed out waiting for Vite on http://localhost:1420\n' >&2
+    exit 1
+fi
+
+printf 'Vite ready. Launching Tauri...\n' >&2
+npx tauri dev --config '{"build":{"beforeDevCommand":""}}' "$@"