perf(client-runtime): halve server config bootstrap traffic

[Adamulek123]

What changed

Client sessions now open subscribeServerConfig once and use its first snapshot for initial configuration. The same stream continues to deliver later configuration updates.

Why

Session startup previously called serverGetConfig and then subscribed to server configuration. The subscription's first frame repeated the same full payload, so every connection paid for two bootstrap exchanges. This change keeps configuration fresh without relying on a cache.

Measured impact

Compared with main-latest.json from main commit 230c5d4a:

Server config bootstrap	Main	This PR	Change
WebSocket wire	10,617 B	5,333 B	-5,284 B (-49.8%)
WebSocket decoded	10,597 B	5,323 B	-5,274 B (-49.8%)
Messages	4	2	-2 (-50.0%)

The general thread-transfer measurements remain within 0.2% wire variance. Every enforced ceiling passes.

Validation

• vp test run packages/client-runtime/src/rpc/session.test.ts packages/client-runtime/src/rpc/client.test.ts packages/client-runtime/src/state/server.test.ts, 28 tests passed
• vp exec tsc -p packages/client-runtime/tsconfig.json --noEmit
• Focused lint and formatting
• Deterministic transfer and server-config benchmark guards

Checklist

• This PR is small and focused
• I explained what changed and why
• No UI changes

Generated with GPT-5.6 Sol through the Codex harness.

Note

Reuse session serverConfigEvents stream for subscribeServerConfig to halve bootstrap traffic

• RpcSessionFactory.make now bootstraps initial config from a streaming subscribeServerConfig snapshot instead of a unary serverGetConfig call, then publishes subsequent updates through a session-level serverConfigEvents stream.
• subscribeDynamic in client.ts detects the subscribeServerConfig tag and reuses the existing session stream, avoiding a duplicate RPC subscription.
• New applyServerConfigEvent helper incrementally derives updated ServerConfig from snapshot, keybindingsUpdated, providerStatuses, and settingsUpdated events; mapSessionRpcError maps subscription errors to ConnectionAttemptError.
• Risk: initial config now depends on receiving a snapshot event from the stream; if the stream ends before a snapshot, the connection fails with a remote-unavailable error instead of falling back to serverGetConfig.

^{Macroscope summarized 66ee0d2.}

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Note

Medium Risk
Changes environment connection bootstrap and readiness timing (initial config waits on the first stream snapshot); mistakes could break config sync or duplicate subscriptions, though behavior is heavily covered by tests.

Overview
Session connect now bootstraps configuration from a single subscribeServerConfig subscription instead of serverGetConfig plus a second subscribe, cutting duplicate full-config traffic on connect.

RpcSession forks that subscription once, resolves initialConfig from the first snapshot, and exposes serverConfigEvents as a shared stream (PubSub + replay) that folds keybindingsUpdated, providerStatuses, and settingsUpdated into live config and emits synthetic snapshots when subscribers miss revisions.

subscribeDynamic routes subscribeServerConfig through the session stream when present so callers do not open another websocket subscription. Tests cover no duplicate subscribe, multi-subscriber broadcast/replay, and updated bootstrap expectations.

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[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This changes production connection bootstrap and ongoing server-config delivery by introducing a shared replaying stream with buffering, folding, and new lifecycle/error semantics. The performance gain is well targeted and tested, but the stateful cross-cutting runtime behavior is substantial enough to require human review.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

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