feat(tui): the status row is drawn from what the client knows - #19

…sion 6) (#18)

## Summary

`zypi export <id>` read the session files of the old Rust agent, so it failed for every session that the Python agent stored. It now asks the agent, as a resume does. This is plan decision 6, option (a).

```text
zypi export <id>
  connect()                              # starts the Python agent
  session/load(id, cwd)
    collect session/update (isReplay)
    done when: the answer came AND no replayed update came for 500 ms
    before the answer: 60 s of silence is an error
  AcpUpdateTracker -> ScrollbackState -> render_blocks_to_markdown   # same path as /export
  AgentProcessGuard drop: cancel + join    # also when the command fails
```

```diff
 pi-pager/src/
-├── export_cmd.rs        # read the old Rust session store
+└── export_cmd/
+    ├── mod.rs           # entry and rendering
+    ├── replay.rs        # agent and collection of the replayed updates
+    └── tests.rs         # 18 tests, paused tokio clock
```

The answer to `session/load` can come before the last replayed messages. So the answer alone does not end the collection: only the quiet period does, and only a replayed update restarts it. Permission requests get `Cancelled`, other requests from the agent get method-not-found. `isReplay` is read from the notification `_meta` and from the update `_meta` (the Python agent sets it on the update).

## Evidence

- **Before:** `resume_matrix.py` on `main` (plan section 10.12): 10 PASS / 3 GAP. Case 12, `zypi export <id>`, was GAP: `Session '<id>' not found.`, exit 1.
  **After:** 11 PASS / 2 GAP / 0 FAIL on WSL2. Case 12 passes. Case 13 (unknown id) passes as before. The two GAP that remain are `--resume <title>` and `--session-id <id in use>`; this PR does not touch them. Cases 12 and 13 now also fail when a process is left behind.
- **Time** (debug build, WSL2; three runs each, the session file is not changed):

  | Entries | File | `zypi export` | Agent alone (`session/load`) |
  |---|---|---|---|
  | 2,000 | 1.4 MB | 2.5 s | 0.24 s |
  | 5,000 | 3.6 MB | 5.6-5.7 s | 0.53 s |
  | 20,000 | 14.2 MB | 62.7-64.1 s | 2.5 s |

  The agent is fast. The rest is `zypi` turning the messages into text, and that grows faster than the size. A release build was not measured.
- **Tests:** 18 unit tests in `export_cmd::tests`. 15 run on a paused tokio clock: they cover the order of the updates, the quiet period, the silence limit, requests from the agent, refusals, and an agent that exits or says nothing. 3 cover the rendering. 1 end-to-end test, `export_replays_a_stored_session_through_an_agent_of_its_own`, against the real Python agent; `python_agent_e2e` passes 11 of 11. 1 new test in `scripts/tests/test_tui_pty.py`.
- **Checks that ran locally** (on the code of the final commit; the last edits were documentation only): `tui_baseline.py check` exit 0 (warnings 0, residue words unchanged, dependency graph 980 = ceiling, `cargo check --workspace --tests` 0 errors). `ruff check` and `ruff format --check` pass. `pytest`: Windows 2,517 passed, 39 skipped, 31 deselected; WSL 2,540 passed, 16 skipped, 31 deselected.
- **CI** (on `e3f3458`: [TUI CI run](https://github.com/zy1233/pi-python/actions/runs/38344799030), [CI run](https://github.com/zy1233/pi-python/actions/runs/38344799403)): every job passes. `Ruff`. `pytest` 3.11, 3.12 and 3.13. `Gates + cargo check`: warnings 0, `leader` 245 of 245, `x.ai` 304 of 304, graph 980 of 980. `cargo test`: 8,684 passed, 0 failed, 22 ignored (`pi-pager`: 5,627 passed, 13 ignored). `Release build baseline` is manual and was skipped.
- **Not verified:** Windows and macOS (only WSL2 ran `zypi export`). Release-build time. A real model (the agent is a mock; export does not call the model).
- **Found, not fixed** (details in plan section 10.15, "continuation 6"): the Python agent loops forever on a session file with repeated entry ids; `scripts/session_list_bench.py` writes such a file above 4,096 entries; the pager reads `isReplay` only from the notification `_meta`, the agent sends it on the update (the resume path was not checked).

## Merge Danger

**Door:** two-way

The change reads session files and writes none. A revert restores the old behaviour, which fails for every session of the Python agent.

**Blast Radius:** export

`zypi export` now needs a working agent command, as a resume does; it did not before. A very large session takes about a minute on a debug build. Nothing else in the pager changes. The new `test-util` feature of `tokio` is a dev-dependency only.

Merged on the owner's order, into V0.5 (`v0.5.0`). The CHANGELOG entry moves from `[Unreleased]` to `[0.5.0]`, and the `zypi export` line leaves the known issues, in the commit that follows (it is part of #19, which merges after this PR). `tui/` changed, so the release size is measured again on the final tree (`release_baseline`, condition 2) and CI must pass on the tag commit (condition 1).

… r12, part 8) (#20)

The owner asked to merge #18 and #19 and to put both into V0.5. Both are on
main now (ec7d455 and 9058ab3). This commit moves their two CHANGELOG
entries from [Unreleased] to [0.5.0], because the release page shows only
the section of the tag's version.

- CHANGELOG.md: the Fixed entry (zypi export) and the Changed entry (status
  row) move into [0.5.0]. The date is the release day (2026-10-13). The known
  issue about zypi export goes. The known issue about [ui.status_line] now
  says what is left: no context or cost items. Release notes preview with the
  awk program of release.yml: 49,429 B, five groups.
- Plan: the status of exit conditions 1 to 3 on the final tui/ tree (CI and
  TUI CI green on 1fa18cf and on main, zypi 420,667,200 B, release dry run
  green), the new status of decisions 6 and 15, and the known issues.
- Execution log: part 8.
- docs/baselines/tui.md: the new release size and build time.

Local pytest and cargo tests were not run again, as the owner asked. Ruff
passes. CI ran the tests on the same tui/ and packages/ trees that the tag
will have, because this commit changes documents only.

…raws nothing (#21)

The Added entry for scripts/tui_pty/status_line_probe.py said that the row
draws nothing with the Python agent. #19 changed that, and the Changed entry
of the same release says so. The release page would have shown both. The
entry now says what the probe found when it was written and what it checks
now.

I searched the [0.5.0] section for other lines that #18 or #19 made old, with
these words: export, status_line, status row, session_status, resume_matrix,
GAP, probe, tui_pty. This was the only one.

The release notes grow from 49,429 B to 49,640 B (awk program of
release.yml). The plan and the execution log have the new number.