[AmirF194]

Summary

IdeaTree.prune_node() recursively sets status = "pruned" on the target node and every
descendant (_prune(), called on node_id then each child_id), but after the recursion
finished it emitted exactly one IDEA_PRUNED event, for node_id only.

Every consumer keys off a single node_id per event: StatsCollector._inc_pruned increments
a counter by one per event, and RunState.on_idea_pruned (the source for the TUI header and,
via webui/snapshot.py, the WebUI tree) updates the record for the one node_id in the event
payload. So cascaded descendants kept their pre-prune status ("proposed") in both places even
though idea_tree.json on disk already marked them pruned, which is the TUI/WebUI count
mismatch reported in #62.

Fix: collect the ids mutated during the cascade and emit one IDEA_PRUNED event per id instead
of one for the whole cascade. Each descendant now carries the same reason as the node the
caller pruned, since it was pruned as a direct consequence of that call.

Linked issue

Closes #62

Type of change

• Bug fix (fix)

How was this tested?

• New regression test asserts the event set matches every mutated node id (not just the
  target) and that an untouched sibling emits nothing; both fail against unpatched
  prune_node and pass after the fix.
• A second test drives StatsCollector and RunState end to end through the real event bus
  and asserts the pruned count and every descendant's status.
• Full pytest (154 files) and ruff check src/ tests/ both pass clean on Python 3.10 and
  3.13, in a clean Docker container, with dependency versions pinned from uv.lock.

python -m pytest tests/ -q
python -m ruff check src/ tests/

Not checked: the live TUI/WebUI rendering itself, since neither has a scripted test harness in
this repo; the assertion is on the state each of them consumes (RunState/StatsCollector).

Checklist

• PR title follows Conventional Commits (e.g. fix(config): ...).
• The change is focused and reasonably small.
• I ran the relevant tests locally (python tests/test_*.py) and they pass.
• Docs / examples updated if behavior or config changed. (not applicable, no docs describe this event contract)
• No secrets, API keys, or tokens are included in the diff.