paseo-omp: consume nested provider subagent link support

[omercnet]

Context

The full Docker compatibility canary added in #65 exposed that nested OMP subagents were flattened by Paseo core. The plugin already emits the correct parentSessionId, but Paseo 0.8.0 discards that relationship when publishing provider subagent descriptors.

Upstream issue getpaseo/paseo#4920 was fixed by getpaseo/paseo#4970 (merge commit a8a8da0472c8a1858c65b8bb3a8c166e6ae9efe1). That change also adds optional toolCallId support to provider session.opened events. Upstream did not run this repository's external-provider Docker canary.

The currently published @getpaseo/plugin package and the canary base image are still pinned to Paseo 0.8.0, so this work must consume the first published Paseo release containing #4970.

Work

• Bump @getpaseo/cli, @getpaseo/client, @getpaseo/plugin, and @getpaseo/protocol together to the first release containing fix(plugins): preserve nested provider subagent links getpaseo/paseo#4970.
• Update paseo-omp/canary/Dockerfile to the matching official Paseo image and immutable digest.
• Include toolCallId: ref.parentToolCallId when OmpSubsessionProjector emits a child session.opened event.
• Strengthen the full Docker canary to verify both ancestry and spawning-tool links.
• Run the canary against OMP 18.1.15 and 18.2.0 and record the results.
• After both versions pass, promote the full Docker canary from local-only coverage to a required CI compatibility gate.
• Update compatibility documentation to record the fixed Paseo boundary and verified versions.

Release Please owns package versions and changelog entries. Do not manually edit release-managed version or changelog files.

Acceptance criteria

• A direct OMP child has parentSubagentId: null and a non-null toolCallId matching its root task call.
• A nested OMP child has parentSubagentId equal to its direct parent's public subagent ID and a toolCallId matching the nested task call.
• Direct and nested child timelines remain independently addressable and both children finish as completed.
• The full Docker canary passes with OMP 18.1.15 and 18.2.0 on the released Paseo image containing #4970.
• The promoted CI gate is required before changing the supported OMP floor.