refactor(provider-pi): move Pi into its own provider package

[juliusmarminge]

Pi is the first provider in its own package, @t3tools/provider-pi, following the convention the other drivers will use:

• ./settings: the instance settings schema, moved out of contracts.
• ./client: the client definition with label, settings form, and a plain-data icon (no React). Web and mobile render the icon from the package instead of hand-drawn Pi branches.
• ./server: the driver and adapter driver the server registers.

Pi's server code now imports only provider-core, contracts, and shared, and reaches the server through ProviderHost. The managed status provider, its snapshot-settings source, the context handoff budget, and provider continuation requests move into provider-core so the package can use them. The adding-a-provider checklist now describes the package layout.

Not checked in a running client: the Pi icon should look identical in light and dark mode on web and mobile.

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Part of the provider-packages stack: #17282 → #17283 → #17284 → #17285 → #17286 → #17287 → #17288.

Done by Claude Opus 5.5 in Claude Code.

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	5.0 KiB	—	6.8 KiB	✅
Codex	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Codex	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Codex	Live turn WebSocket decoded	—	20.9 KiB	—	29.3 KiB	✅
Codex	Live turn messages	—	2	—	8	✅
Claude	Total thread wire	—	5.0 KiB	—	6.8 KiB	✅
Claude	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Claude	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Claude	Live turn WebSocket decoded	—	21.2 KiB	—	29.3 KiB	✅
Claude	Live turn messages	—	1	—	8	✅

Baseline: unavailable · PR result: 75f62f8 · Source CI: failure

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[juliusmarminge]

Superseded by the squashed 3-PR stack #17299 → #17300 → #17302 (same changes, regrouped; Effect service modules renamed to PascalCase).