Stack the parallel-in_progress change on the web todo display (#497): the
GUI is now the surface where several active items are visible, so the two
land as a chain rather than colliding on tool-todo at merge time.
Conflicts combined rather than resolved to one side: tool-todo keeps this
branch's parallel-allowing validation AND web2-todo's additionalProperties
unknown-key rejection, in src/index.ts and both README sides; the spec
drops web2-todo's 'two in_progress' rejection case and keeps its unknown-key
case; the two headless advanced-toolchain session fixtures keep this
branch's parallel transcripts.
The origin/master merge added the session-query-spill and
escalation-approved acp scenarios, whose pinned tool-schemas still
carried additionalProperties: true on the todo_write item schema. This
PR tightens that to false (model-visible via the request header), so
re-record it in the two new expected outputs. session-sandbox-root,
escalation-rejected, and fs-escalation-approved compare against the
escalation-approved pinned header and pass once it is fixed.
Remove the single-in_progress cap from todo_write execute validation and
the durable-log invariant so a task list can mirror genuinely parallel
work (concurrent subagents, background commands). Update the tool
description to instruct marking every actively worked task in_progress,
refresh the tool catalog and keyless snapshot expected outputs, and
record the decision in a new Agent Note superseding the original cap.
