Persistent bash keeps the backend's controlled prompt
持久 bash 保留后端的受控提示符
`dsh-tool-bash-persistent` initialized its shell with `stty -echo; PS1='__DSH_PERSISTENT_BASH_PROMPT__ '`, overwriting the `PS1` that `dsh-terminal-bash` sets in the spawn environment. The backend's prompt readiness requires the printable tail after the OSC `133;D` marker to exactly equal the controlled prompt ([design](../feature/2026-07-16-persistent-pty-sessions.md)), so after initialization no send could ever set
English
Problem
dsh-tool-bash-persistent initialized its shell with stty -echo; PS1='__DSH_PERSISTENT_BASH_PROMPT__ ', overwriting the PS1 that dsh-terminal-bash sets in the spawn environment. The backend's prompt readiness requires the printable tail after the OSC 133;D marker to exactly equal the controlled prompt (design), so after initialization no send could ever settle through it. PROMPT_COMMAND survived the override, so the marker kept arriving and every send paid the silence tier plus handoff grace — 3.5 s per tool call under production defaults, 7.2 s for the first call because the initialization send degraded too, and an extra 3.5 s tail after every long command. macOS has no exact stdin-wait tier, and on Linux the exact probe cannot observe a sub-poll-interval command leaving its stdin wait, so the degradation applied to effectively every call. Package tests masked it by configuring idleSilenceMs: 100.
The override existed to give the tool a known prompt for two consumers: a viewport-suffix fallback that detected "shell at a prompt without the end marker", and cosmetic stripping of prompt text from partial output.
Decision
The backend owns its prompt protocol and repairs it itself: the controlled PROMPT_COMMAND re-asserts PS1 after printing the marker, so any in-shell prompt override — this tool's former initialization, a model command, a sourced script — lasts zero prompts. This also protects providers that cannot report foreground state, where the exact prompt text is the only readiness evidence.
The tool stops overwriting PS1 (initialization is stty -echo alone) and replaces its viewport-suffix fallback with the seam's existing signal: a send that settles as stdin_read without the end marker in scrollback returns the captured partial output. The private prompt constant and its stripping are deleted; partial output may now end with the backend's own prompt text, which the tool cannot and should not know.
Alternatives considered
Fix only the tool, leaving PROMPT_COMMAND unchanged. Rejected because the seam would stay silently fragile: any later consumer or model command that touches PS1 reintroduces the 3.5 s degradation with no failing signal, and providers without foreground inspection lose their only readiness factor.
Import the controlled prompt into the tool. Rejected because the prompt is one provider's protocol constant; a Consumer matching it would couple the tool to dsh-terminal-bash specifically, and any other mounted backend would break it again.
Drop the prompt-text factor from backend readiness. Rejected because for providers whose inspectForeground reports nothing, marker-plus-text is the defense against command output that embeds the raw OSC marker sequence; weakening it trades a fast path for a false-settle risk.
Widen handoffGraceMs/idleSilenceMs tuning instead. Rejected because no silence value fixes a dead fast path; it only rebalances how much every call overpays.
Consequences
Measured on darwin with production defaults: raw sends settle in ~86 ms with the controlled prompt intact versus ~3540 ms after an override; tool calls drop from 7180/3560/3566 ms to 355/88/91 ms for spawn+init+echo, echo, and pwd.
The stdin_read fallback is behavior, not only cosmetics: after exec, an interrupt, or an interactive foreground child whose stdin wait the provider proves (the Linux exact tier), the call now returns captured partial output instead of spinning to the command deadline. Where no provider proves the wait (macOS), an interactive child still runs to timeoutMs — recorded as a known limitation in the tool README. Partial output can carry the backend's trailing prompt; complete marker-delimited output is byte-identical to before, which the keyless jsonrpc-agent snapshots confirm.
The loader-composition suite now sets idleSilenceMs above the send bound, so silence can settle nothing and every case fails if prompt readiness regresses; a real-PTY case overrides PS1 in-shell and requires the next send to settle as stdin_read with the healed prompt. The self-repair cannot survive a command that overwrites PROMPT_COMMAND itself; the silence tier remains the bound there, unchanged from the prior design.
中文
Problem
dsh-tool-bash-persistent 用 stty -echo; PS1='__DSH_PERSISTENT_BASH_PROMPT__ ' 初始化其 shell，覆盖了 dsh-terminal-bash 在 spawn 环境中设定的 PS1。后端的提示符就绪检测要求 OSC 133;D 标记之后的可打印尾部与受控提示符完全相等（设计），因此初始化之后任何 send 都无法经由该路径结算。PROMPT_COMMAND 未被覆盖，标记仍持续到达，于是每次 send 都要支付静默层加交接宽限——生产默认值下每次工具调用 3.5 秒；首次调用 7.2 秒，因为初始化 send 同样退化；每条长命令结束后还要多等 3.5 秒。macOS 没有精确 stdin 等待层，而 Linux 的精确探测无法观察到在一个轮询周期内完成的命令脱离其 stdin 等待，因此退化实际覆盖了几乎每次调用。包测试把 idleSilenceMs 配成 100 毫秒，掩盖了该问题。
这个覆盖存在的目的是给工具一个已知提示符，服务两个消费点：用视口后缀检测「shell 已回到提示符但没有结束标记」的回退判定，以及从部分输出中剥离提示符文本的美化。
Decision
后端拥有自己的提示符协议并自行修复：受控 PROMPT_COMMAND 在打印标记后重新设定 PS1，因此任何 shell 内的提示符覆盖——本工具从前的初始化、模型命令、被 source 的脚本——都存活不到下一个提示符。这同时保护了无法报告前台状态的提供方：在那里，确切的提示符文本是唯一的就绪证据。
工具不再覆盖 PS1（初始化只剩 stty -echo），并用 seam 已有的信号替换其视口后缀回退：一次以 stdin_read 结算而 scrollback 中没有结束标记的 send，返回已捕获的部分输出。私有提示符常量及其剥离逻辑删除；部分输出现在可能以后端自己的提示符文本结尾，工具无法也不应知道该文本。
Alternatives considered
只改工具，不动 PROMPT_COMMAND。 被拒绝：seam 仍然静默脆弱——之后任何触碰 PS1 的消费方或模型命令都会在没有失败信号的情况下重新引入 3.5 秒退化，且无前台检查的提供方失去唯一的就绪因子。
把受控提示符导入工具。 被拒绝：提示符是单个提供方的协议常量；Consumer 匹配它就把工具与 dsh-terminal-bash 具体耦合，换任何其他后端都会再次损坏。
从后端就绪检测中去掉提示符文本因子。 被拒绝：对 inspectForeground 无法报告任何信息的提供方而言，标记加文本是对抗「命令输出中嵌入原始 OSC 标记序列」的防御；削弱它是拿误结算风险换快速路径。
改为调大 handoffGraceMs/idleSilenceMs。 被拒绝：任何静默值都修不好已死的快速路径，只是重新分配每次调用多付多少。
Consequences
darwin 上以生产默认值实测：受控提示符完好时裸 send 约 86 毫秒结算，覆盖后约 3540 毫秒；工具调用从 7180/3560/3566 毫秒（spawn+init+echo、echo、pwd）降至 355/88/91 毫秒。
stdin_read 回退是行为而不只是美化：在 exec、中断，或提供方能证明其 stdin 等待的交互式前台子进程（Linux 精确层）之后，调用现在返回已捕获的部分输出，而不是空转到命令期限。没有提供方证明该等待时（macOS），交互式子进程仍会运行到 timeoutMs——已记入工具 README 的已知限制。部分输出可能带有后端的尾部提示符；由标记界定的完整输出与之前逐字节相同，无密钥 jsonrpc-agent 快照确认了这一点。
loader 组合套件现在把 idleSilenceMs 设在 send 上限之上，静默无法结算任何 send，提示符就绪一旦回归，每个用例都会失败；一个真实 PTY 用例在 shell 内覆盖 PS1，并要求下一次 send 以 stdin_read 结算且提示符已修复。自我修复无法在 PROMPT_COMMAND 本身被覆盖的命令后存活；那里静默层仍是边界，与先前设计一致。