fix(tui): make the dashboard immune to stray console output

AGENTS.md

@@ -475,6 +475,33 @@ The patched llama.cpp staged runtime has its own ABI version, tracked in `skippy
 
 For changes in `crates/mesh-llm-ui/`, use components and compose interfaces consistently with shadcn/ui patterns. Prefer extending existing primitives in `src/components/ui/` over ad-hoc markup.
 
+### Terminal dashboard integrity
+
+The dashboard renders to the **controlling terminal** (`/dev/tty`, `CONOUT$`),
+never to fd 1 or fd 2, and while it owns the screen those two descriptors are
+redirected into it (`crates/mesh-llm-tui/src/output/console_capture.rs`). Stray
+`println!`/`eprintln!`, inherited child stderr, and native llama.cpp output
+therefore arrive as dashboard events instead of painting over the frame.
+
+Consequences worth knowing before changing this area:
+
+- Do not point the TUI backend, or the enter/exit escape writers, at
+  `io::stderr()`. Capture would then redirect the dashboard into its own pipe.
+- Anything restoring the terminal (panic hooks, emergency writers) must release
+  the capture *before* writing, or the message goes into the pipe.
+- Capture cannot intercept a write to the tty by a process that did not inherit
+  our descriptors. `R` is the repair for that case: a physical clear plus a
+  ratatui diff invalidation. A logical `Clear` widget does not fix backend
+  desynchronization.
+- Do not perform that clear on every draw. It repaints from blank and reads as
+  a black blink; measured on an idle dashboard it was ~2.6 full repaints/s.
+
+Prefer `OutputEvent` or `tracing` in runtime code regardless — captured lines
+have no level and are shown with a `stdout` context. When adding a `tracing`
+target that must reach the dashboard, add a directive for it in
+`runtime_tracing_subscriber`: `EnvFilter::from_default_env()` defaults to ERROR,
+so an unlisted target's `warn!` is dropped before the writer sees it.
+
 ## Testing
 
 Read `docs/design/TESTING.md` before running tests. It has all test scenarios, remote deploy instructions, and cleanup commands.

crates/mesh-llm-host-runtime/src/runtime/tracing_writer.rs

@@ -318,8 +318,11 @@ pub(super) fn init_runtime_tracing() -> Result<()> {
 pub(super) fn init_embedded_runtime_tracing() -> Result<()> {
     let subscriber = runtime_tracing_subscriber()?;
     if let Err(err) = tracing::subscriber::set_global_default(subscriber) {
-        eprintln!(
-            "mesh-llm embedded runtime using existing tracing subscriber; could not install mesh-llm subscriber: {err}"
+        // The host already had a subscriber, so this warning has somewhere to
+        // go. Writing it raw would put it straight onto the dashboard frame.
+        tracing::warn!(
+            error = %err,
+            "mesh-llm embedded runtime using existing tracing subscriber"
         );
     }
     Ok(())

crates/mesh-llm-tui/Cargo.toml

@@ -24,3 +24,8 @@ ratatui = "0.30"
 serde_json.workspace = true
 tokio = { version = "1", features = ["macros", "rt", "sync", "time"] }
 tracing = "0.1"
+
+[target.'cfg(unix)'.dependencies]
+# Safe wrappers for the dup/dup2/pipe plumbing behind console capture. Used in
+# preference to raw libc so this crate keeps `#![forbid(unsafe_code)]`.
+rustix = { version = "1", features = ["event", "stdio"] }