fix(omp): keep parent non-idle while internal task subagents run (port of upstream #3371)

[joeshull]

Upstream issue: getpaseo#2232
Upstream pull request: getpaseo#3371
Upstream head repository: jasonhnd/paseo
Upstream head: fa9fc5e

Direct import of upstream getpaseo#3371. Both commits are @jasonhnd's, unmodified: this branch is that pull request's head commit exactly, so the fork and upstream patch sets are identical in content and order.

What it does

OMP can end the parent model loop (agent_end + !isStreaming && !isCompacting) while internal task children are still writing, so Paseo marked the parent idle while work continued (upstream getpaseo#2232).

1. Idle gate. Do not complete the turn until the subagent index reports no running children.
2. Snapshot reconcile. A successful get_subagents reply lists only still-running children, so an id that previously appeared and is now missing is treated as completed. A child seen only via lifecycle is not killed by an empty first reply.
3. Deferred task cards. OMP's task tool_execution_end is a dispatch acknowledgement, not a result, so the card stays open until the index has a linked child and none are running.

Adds validated get_subagents RPC support to the CLI runtime.

Why import it now

Upstream getpaseo#3371 is still open and changes the same function as #25. Importing it first keeps the two changes from colliding and lets #25 rebase onto internal/main afterwards. Upstream getpaseo#3371 replaces the closed upstream getpaseo#2245, which review rejected because snapshot reconcile never treated a disappeared get_subagents id as terminal — the stuck-running-parent risk this rewrite fixes.

Preflight

node scripts/check-upstream-port.mjs \
  --candidate omp-idle-gate-3371 \
  --upstream-ref 23853a1515d374b873f9d5749b532a81f022b1cd \
  --integration-ref origin/internal/main \
  --allow-path packages/server/src/server/agent/providers/omp
Upstream port preflight passed: 9 changed path(s).

The branch is based directly on upstream main at 23853a151 (verified an ancestor of fetched getpaseo/paseo:main), does not descend from internal/main, and changes only packages/server/src/server/agent/providers/omp.

Verification

Run against this repository's dependencies:

• npx vitest run packages/server/src/server/agent/providers/omp — 19 files, 127 tests pass
• npm run lint on the omp provider — 0 warnings, 0 errors
• npm run format:check — clean

npm run typecheck on the upstream base reports missing-module errors for @replit/codemirror-lang-csharp and @paseo/plugin, which come from resolving this checkout's node_modules against an older lockfile, not from these commits. CI installs from the merge result and is the authority here.

I did not re-verify against a live OMP process; see the upstream pull request for the author's own QA.

Merge order

Merge this first. #25 bounds all three of the gate's wait conditions, including the subagent wait added here, and rebases onto internal/main once this lands.