MCPJVM-370: Public MCP query support for watcher_state

[nimbly-dev]

Description

Once SQLite-backed watcher state exists, Regression Suite needs a public MCP query surface for bounded inspection of persisted watcher lifecycle information. This story exposes watcher_state through artifact_management as a query-oriented state surface for understanding long-running bounded waits, intermediate progress, and final watcher outcomes.

This story should define the public request/response shape, filtering behavior, paging, sorting, and fail-closed behavior for watcher_state queries.

Scope

In scope:

• Add watcher_state as a public artifact_management state surface
• Expose query support for persisted watcher state
• Support bounded filtering by projectName, planName, runId, watcherName, provider type, and watcher status
• Support deterministic paging and sorting for watcher histories and long-running flows
• Keep the public surface query-oriented and read-only for runtime-owned rows

Out of scope:

• Watcher runtime execution semantics themselves
• Storage implementation internals
• Manual mutation of runtime-owned watcher rows
• Legacy migration/backfill semantics

Acceptance Criteria

• artifact_management supports public query access for watcher_state
• Query behavior is bounded, deterministic, and fail-closed
• Watcher-specific lookup fields are supported in the public contract
• Paging and sorting are supported for large or long-running watcher histories
• Response output is sufficient for agents/users to inspect bounded watcher progress and terminal outcomes without loading full Artifact history by default

Implementation Notes

• Ensure query results can represent pending, in_progress, ok, fail_closed, and timed_out style watcher outcomes cleanly.
• Keep the public shape useful for observing multi-pass execution where tooling timeout limits may prevent one long synchronous orchestration call.

Testing

• UT for watcher_state query validation and watcher-specific filter normalization
• UT for paging/sorting behavior on watcher histories
• IT for querying intermediate and terminal watcher states
• IT for fail-closed behavior on invalid watcher query inputs