docs(pty): move the settled-send output contract to its declaring seam

The Agent Note paragraph recorded test-specific timing advice, which
docs/AGENTS.md excludes from implemented notes. The durable half of it —
LocalSendOperation.append drops output after settle, so it survives only in
the scrollback — now documents append itself.

.agents/notes/implemented/feature/2026-07-16-persistent-pty-sessions.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write .agents/notes/implemented/feature/2026-07-16-persistent-pty-sessions.md
-2026-07-16-persistent-pty-sessions.md: 16277ccc8a5a5afc47e9aade420dedcaad862d68
-2026-07-16-persistent-pty-sessions.zh.md: 26197fbd76e2f3be6e85786fbef5e73bce9f3e55
+2026-07-16-persistent-pty-sessions.md: 8c6d317f5b2a264bc946030f37084fb839f8f0d8
+2026-07-16-persistent-pty-sessions.zh.md: 105e756f09e1910901429ff5836e57030d70b122

.agents/notes/implemented/feature/2026-07-16-persistent-pty-sessions.md

@@ -80,8 +80,6 @@ On macOS there is no exact syscall tier. Output silence returns `inferred_idle`
 
 Tier 2 returns `inferred_idle` after `idleSilenceMs` without output. A sleeping or network-blocked command can therefore look ready. When a prompt marker was already seen, Tier 2 waits a further `handoffGraceMs` so a bash foreground handoff that lands on the silence boundary still settles as the exact `stdin_read` attribution instead of the weaker inference; the grace is a deployment-owned config field validated to cover at least one `pollIntervalMs`, because a grace shorter than the poll period cannot contain a single readiness poll and so cannot change any outcome. It bounds only sends that saw a marker, so its cost is the interactive return latency of that one case rather than every send. Tier 3 returns `timeout` after `timeoutMs` so a foreground tool call cannot hold the agent indefinitely. The result preserves the distinction; callers may wait through `ctx.tasks`, signal the foreground group, or inspect from another session.
 
-Once a send settles under any tier, `PtySendOperation.append` stops accepting output, so later child output reaches only the scrollback. A test that waits for a marker on the operation must therefore set `idleSilenceMs` and `timeoutMs` above the child's own startup latency; interpreter startup on a loaded macOS runner otherwise ends the send before the marker is printed.
-
 `node-pty` data notifications feed one terminal parser. Parser carry state handles control sequences and a trailing carriage return split across callbacks, so a divided CRLF produces one newline rather than a pagination-changing blank line. The implementation normalizes line-oriented output, but it does not promise correct interaction with a full-screen application.
 
 ### Model-visible output and durability

.agents/notes/implemented/feature/2026-07-16-persistent-pty-sessions.zh.md

@@ -80,8 +80,6 @@ macOS 没有精确 syscall 层。任何前台进程组输出静默都会返回 `
 
 Tier 2 在持续 `idleSilenceMs` 没有输出后返回 `inferred_idle`，因此 sleep 或网络阻塞的命令可能看似 ready。如果此前已经见过 prompt marker，Tier 2 会再等待 `handoffGraceMs`，使恰好落在静默边界上的 bash 前台交接仍然以精确的 `stdin_read` 归因结束，而不是退到较弱的推断；该宽限是由部署方拥有的配置字段，并被校验为至少覆盖一个 `pollIntervalMs`——短于轮询周期的宽限装不下一次就绪轮询，因此不可能改变任何结果。它只约束见过 marker 的 send，代价是这一种情况的交互返回延迟，而不是每一次 send。Tier 3 在 `timeoutMs` 后返回 `timeout`，避免前台工具调用无限占住 agent。结果保留这些区别；调用方可以通过 `ctx.tasks` 等待、向前台组发信号，或从另一个会话排查。
 
-一次 send 在任一层级 settle 之后，`PtySendOperation.append` 就不再接受输出，此后子进程的输出只会进入 scrollback。因此，在 operation 上等待标记的测试必须把 `idleSilenceMs` 与 `timeoutMs` 设得高于子进程自身的启动耗时；否则在负载较高的 macOS runner 上，解释器启动会在标记打印之前就结束这次 send。
-
 `node-pty` data 通知进入同一个终端 parser。parser 的 carry state 会处理跨 callback 的控制序列和位于 callback 末尾的回车；因此，即使 CRLF 被拆开，也只会生成一个换行，而不会产生改变分页的空行。实现会规范化行式输出，但不承诺正确操作全屏应用。
 
 ### 模型可见输出与持久性

packages/pty/pty-local/src/session.ts

@@ -93,6 +93,13 @@ class LocalSendOperation implements PtySendOperation {
     return this.promise.promise
   }
 
+  /**
+   * Accumulate sanitized output into the operation's viewport. Output that arrives after
+   * the operation settles is dropped here and survives only in the session scrollback, so
+   * a caller waiting on this operation for a marker cannot observe one the child prints
+   * after any readiness tier ended the send.
+   * @param text Sanitized text to append while the operation is still active.
+   */
   append(text: string): void {
     if (!this.finished) this.output.append(text)
   }