---
model: claude-opus-4-8
service: claude
session: c7860302-6a33-4d92-821c-0807d68be464
timestamp: 2026-07-02T22:25:44Z
git_ref: 9201a2ed
scope: code
substantive: true
raw_file: 20260702T222544Z_9201a2ed_prompt_io.raw.md
---

## Prompt

Continuing on branch `drop_ria_nursery` after step B
(`9201a2ed`). User green-lit the deferred error-handler merge:

> yes, i checked us out on a new branch for the ria-tn removal;
> work off the new wkt branch drop_ria_nursery.

and (re the migration) "nope, later we'll do this", plus:

> do ensure the test suite is green in the current state and
> those going forward ya?

and the standing reminder: no commits without a human ack.

## Response summary

Step B2 of the `._ria_nursery` removal (issue #477): merge the
two nested error handlers in
`_open_and_supervise_one_cancels_all_nursery` into one, now
that the 2ndary nursery (whose `__aexit__` the outer handler
originally guarded) is gone.

Trace-driven justification (see
`ai/conc-anal/ria_nursery_removal_plan.md` Step-B2 section):
the old inner handler records `errors[uid]` as its FIRST
action, so `errors` is always non-empty by the time control
could reach the outer handler — making the outer handler's
`raise` DEAD (always superseded by the `finally`'s
raise-from-`errors`). Collapsing to a single
`except BaseException as _scope_err` + the existing `finally`
is therefore behavior-preserving.

- removed the outer `try` + the
  `except (Exception, BaseExceptionGroup, trio.Cancelled)`
  handler; de-indented the inner handler one level.
- dropped the now-unused `outer_err`/`inner_err` locals
  (single `_scope_err`).
- net ~30 lines lighter.

Gated hard: baseline (pre-B2 tip) = 300 passed + 1
load-induced `TooSlowError` flake (passes 6/6 in isolation);
B2 error/cancel gate (`test_cancellation remote_exc_relay
inter_peer_cancellation advanced_faults oob_cancellation
to_actor spawning local rpc`) = 71 passed, 1 xfailed; B2
full-suite run following.

## Files changed

- `tractor/runtime/_supervise.py` — collapse the two handlers
  into one; drop `outer_err`/`inner_err`

## Human edits

None yet — committed via the drafted
`.claude/git_commit_msg_ria_b2.md` (user-driven
`git commit --edit`).