fix(pty): keep the controlled prompt so persistent bash settles fast

tool-bash-persistent overwrote the backend's PS1, so terminal-bash prompt
readiness never matched and every send degraded to the 3.5s silence tier
(idleSilenceMs + handoffGraceMs) under production defaults.

The controlled PROMPT_COMMAND now re-asserts PS1 before every prompt, so an
in-shell override never survives to the next prompt. The tool initializes
with stty -echo alone and detects the no-end-marker fallback through the
seam's stdin_read wait reason instead of matching its own prompt text.

Tool calls drop from 7180/3560/3566 ms to 355/88/91 ms (spawn+init+echo,
echo, pwd; darwin, production defaults). The loader composition suite now
pins the fast path by pushing idleSilenceMs beyond the send bound, and a
real-PTY case proves PS1 self-healing.

Fixes #2585

packages/terminal/terminal-bash/src/index.ts

@@ -60,7 +60,10 @@ function childEnvironment(spec: TerminalBackendSpawnSpec): Record<string, string
     PAGER: 'cat',
     GIT_PAGER: 'cat',
     PS1: CONTROLLED_PROMPT,
-    PROMPT_COMMAND: 'printf "\\033]133;D;%s\\007" "$?"',
+    // Re-asserting PS1 after the marker keeps prompt readiness working when a
+    // command overwrote the shell variable: bash runs PROMPT_COMMAND before
+    // rendering each prompt, so an override never survives to the next prompt.
+    PROMPT_COMMAND: `printf "\\033]133;D;%s\\007" "$?"; PS1='${CONTROLLED_PROMPT}'`,
     BASH_SILENCE_DEPRECATION_WARNING: '1',
     DSH_SHELL: '1',
     DSH_SESSION_ID: spec.owner.id,