Embedded Vibe usage attribution: ACP usage → quota gatherer with call_source=vibe_code parity #1713

Part of the Vibe-embedding epic (ACP-hosted vibe-acp).

Scope

Feed the embedded path's usage into the same quota pipeline the shim feeds today, so the burn plan and marts see one Mistral/Vibe pool regardless of route:

• ACP gives usage in two places (observed 2026-11-05): the session/prompt response (usage: {totalTokens, inputTokens, outputTokens, cachedReadTokens} — spike turn: 16,864 total) and streaming session/update usage_update notifications (used/size context window + _meta steps, prompt/completion/cached tokens).
• Map these onto the fork's usage records and the quota gatherer with attribution parity: embedded turns must carry the same call_source = "vibe_code" metering identity the vibe-direct shim stamps (PR vibe provider: native wire-protocol emulation of the Mistral Vibe binary (no ACP host, no subprocess) #1653), so the Vibe quota marts don't fork by route.
• Plan-state reads (the fetcher landed 2026-11-04/05: keyring-authed whoami + account-context; console-only credits leg) stay as they are — this issue is per-turn usage attribution, not the plan/credits producer. Adjacent: quota: mistral browser-dependent usage read (Vibe plan) — producer + watchdog adapter #1 openchamber#1630 (browser-derived usage figures) and quota aggregator: exempt declared key-validity (console-only) providers from the no-data error degradation developing-today/code#6087 (aggregator display exemption).

Acceptance

• An embedded turn's tokens appear in the gatherer's records within one gather cycle, attributed identically to a shim turn of the same model.
• A side-by-side day of mixed traffic (some sessions shim, some embedded) reconciles to a single Vibe total in the quota view — no double-count, no orphan rows.