Client config reporting — stage 2: full DRIVER_CONFIG report

[nikagra]

What

Stage 2 of driver configuration reporting: fills in the full DRIVER_CONFIG JSON report, replacing the stage-1 {"version":1} placeholder. When advanced.client-config-reporting.enabled = true, the control connection now reports the driver's effective configuration as the cross-driver schema shape.

Stacked on #967 (stage 1). This branch is based on the stage-1 branch, so its diff includes the stage-1 commit until #967 merges — review the second commit (feat: populate the full DRIVER_CONFIG report) for stage-2 changes, and merge after #967.

The report

All 11 groups are populated from the default execution profile and the context's policies, rebuilt on each control-connection init (so it reflects the current, possibly reloaded, config):

• connection / socket / control_pane_settings — timeouts (ms), TCP/socket options. Keys the Java driver has no equivalent for (socket read/write timeout, server-side internal-query USING TIMEOUT) are reported as null.
• reconnection_policy / retry_policy / speculative_execution_policy — a discriminated object selected by the configured policy class (exponential/constant, standard-error-aware/downgrading-consistency, constant/none), with a custom fallback carrying the user policy's class name.
• load_balancing_policy — normalized flags for DefaultLoadBalancingPolicy (token_aware, dc_failover, explicit-vs-inferred local_dc, local_rack, ...); custom otherwise.
• connection_pool / query_defaults / tls — pool sizing + shard-aware port, per-request defaults (page size, consistency, idempotence, client timestamps), and TLS booleans only (never credentials, keystores, or host lists).

Reporting remains fail-safe: any failure while building the report is swallowed; SESSION_ID is still emitted and only the config blob is dropped.

Reconciliation decisions (Java ↔ schema)

• load_balancing_policy.shuffle → false (Java has no replica-shuffle option).
• control_pane_settings.system_query_server_side_timeout_ms → null (Java's metadata timeout is client-side; it does not emit USING TIMEOUT).
• Custom policies → {type:"custom", name:<class simple name>} only (no reflective attribute dump in v1).

Testing

• DefaultDriverConfigReporterTest expanded to 17 tests: the default report shape (golden), each policy discrimination branch, explicit local-dc, server-side timestamps, TLS enabled, socket overrides, unbounded page size, plus the stage-1 gating/fail-safe cases. Report content is asserted against a real config from OptionsMap.driverDefaults().
• Context package + config-consistency + ProtocolInitHandlerTest green.

Follow-up

• Integration test against a live ScyllaDB: connect, SELECT client_options['DRIVER_CONFIG'], client_options['SESSION_ID'] FROM system.clients, assert the JSON is schema-valid and SESSION_ID is identical across a session's rows. (Needs a running cluster; not included here.)
• Confirm the server prerequisite before flipping the flag default on (unknown STARTUP key tolerance + client_options value-length).

🤖 Generated with Claude Code

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