[Stability][BUG-005] Active run token and raw stream observability is insufficient

Parent stability dashboard: #3107

This issue tracks BUG-005 from #3107.

Problem

During a long run, checkpoint message metadata can already contain substantial token usage while the run row/API still shows zero totals.

Evidence

Source: database inspection while the run was still active.

runs.status=running
runs.total_tokens=0
runs.llm_call_count=0
runs.message_count=0

At the same time, checkpoint state already summed to hundreds of thousands of tokens.

Raw stream was also not durably available:

Source: gateway log, run worker stream-mode setup.

'events' stream_mode not supported in gateway (requires astream_events + checkpoint callbacks). Skipping.

Actual stream modes:

['messages', 'custom', 'updates', 'values']

run_events was memory-backed, and no durable run event rows were available after the fact.

Impact

• Operators cannot monitor runaway token cost from normal run records while the run is active.
• After-the-fact debugging depends on checkpoints/logs rather than a durable raw event stream.
• It is difficult to tell whether a long-running task is healthy, stuck, or burning budget.

Expected behavior

• Active runs should expose current token/LLM-call/message counters.
• Raw stream or equivalent trace should be optionally persisted for debugging long tasks.
• Cost visibility should not require manually inspecting checkpoint internals.