fix(*): key a running spawn's live account by its record, not its id alone - #577

…alone (#577)

## Summary

While a spawned sub-agent runs, its live account (transcript, usage,
tool calls) is held in a process-wide index. A spawn was keyed into it
by the node id the model chose, which is unique for one conversation
only, so two conversations running a spawn under the same id shared one
entry: the later `collecting` overwrote it, so the earlier
conversation's context panel showed the other run's transcript (and,
since #567, its live usage), and the first run to finish popped the
entry, so the other run's live view went blank until it ended. This has
been possible since a92514e (2026-09-07), when the spawn record id
became the model's own `node_id`; before that the key was a minted,
globally unique call id.

The key is now the record's own address, the conversation's node root
plus the id (`history.spawn_live_key`, the spawn side of
`dag_store.node_live_key`). The writer holds the root as the record's
directory and the readers as the node files' root, both resolved from
the same session directory, so the two sides agree without depending on
how a session key is spelled. `subagent.context` and `tasks.list` read
by the same helper; the dag side already carried its run id. No wire
change.

## Type

- [x] Fix
- [ ] Feature
- [ ] Docs
- [ ] CI / tooling
- [ ] Refactor
- [ ] Other

## Verification

Run in the fix worktree, base `refactor/ui_web_architecture` at
9656dd9:

- `uv run pytest tests/test_rpc_tasks.py
tests/test_rpc_subagent_calls.py tests/test_subagent_activity.py`: 104
passed. Two tests are new: two conversations running a spawn under the
same id each read their own usage through `tasks.list`, and each read
their own transcript through `subagent.context` driven through a real
`SubagentManager.spawn` with a backend that waits to be released, with
the first run to finish taking nothing of the other's. The second test
was run against the pre-fix source and failed there (conversation A read
conversation B's transcript).
- `uv run pytest tests/test_subagent_manager.py`: 159 passed.
- `make lint-python` and `make test-python`: 23989 passed, 109 skipped.
- Relevant Ruff check and format check: passed.
- Real gateway (`raven serve` from this branch on the user's home,
Raven-Code lane): two conversations dispatched a spawn under the same
`node_id` at once, one saying ALPHA in two steps and one saying BRAVO in
five; polled every 3 s, each conversation's `subagent.context` carried
only its own word while both ran, and after the ALPHA run settled the
BRAVO conversation's live view stayed up and kept growing (6 to 10
messages) instead of going blank. The #567 regression driver on the same
gateway still passed its trace and subtitle checks (tool rows 0, 1, 3, 4
while running; answer landed; subtitle `Raven-Code / done / 1m02s`).
- Real gateway on an isolated `RAVEN_HOME` (in-process `Raven` lane):
the `tasks.list` reader, which now reads by the same key, still served
the live usage -- subtitle `Raven / running / 5s / 1,881 tokens` up to
`Raven / done / 49s / 8,601 tokens`, board chip 1, 2, 3 tools.

## Risk

- [x] Security impact considered: this closes a cross-conversation leak
of a running sub-agent's transcript and usage inside one gateway
process; nothing new is exposed.
- [x] Backward compatibility considered: the key is in-memory only, so
no record on disk changes shape; a reader and a writer of one process
always run the same code.
- [x] Rollback path is clear for risky changes: revert the squash
commit.

## Related Issues

Fixes #580. #567 added the second reader of this index (`tasks.list`)
and gated it to running nodes; the collision itself predates it.

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Co-authored-by: Claude (claude-fable-5-1) <noreply@anthropic.com>