Record metrics for a cancelled stream query

[robinskil]

Parent: #481

Describe the bug

The stream output records query metrics at stream end. A cancelled query never reaches that point.

The query store then holds no row for the query. The atlas_* counters are lost too.

A slow query that a client abandons leaves no trace.

Impact

These queries need diagnosis the most. A user reports a slow query. The query store holds nothing about it.

The two output routes differ here. run_query_to_file records metrics after the write. The code says so at runtime.rs:237.

Expected behavior

A cancelled query records the metrics it collected.

Open decision

The row is partial. A reader must not read it as a complete query.

Pick one option:

1. Add a state column. Values: complete, cancelled.
2. Add a boolean column for a partial row.
3. Mark the row in an existing column.

Option 1 is clearer. It also costs a schema change in the query store.

Suggested fix

1. Pick an option above.
2. Record the metrics when the stream drops.
3. Mark the row with the chosen column.

A Drop implementation on the stream wrapper is one way. CoalesceSqlStream already wraps the stream.

Keep the record step cheap. A drop runs on the runtime.

Files

beacon-db/beacon-core/src/runtime.rs

beacon-server/beacon-server/src/axum/client/query.rs

Scope

Every stream query. The format does not matter.

[robinskil]

Issue #486 adds a registry of active queries. It must decide what the registry reports.

This issue must decide how the query store marks a partial row.

One decision covers both. Sequence the two together.