feat: add Pi provider integration via RPC

[oussamadouhou]

What Changed

• Add Pi as a built-in provider using Pi's native JSONL RPC mode.
• Add provider health checks, configured-binary support, dynamic model discovery, and provider-native thinking options.
• Map Pi session, turn, text, reasoning, tool, approval, and user-input events into T3 Code's canonical provider runtime events.
• Add guarded approval handling, attachments, model switching, rollback/fork behavior, and Pi-backed text generation.
• Surface Pi in provider settings, provider-instance creation, icons, and model selection.
• Add focused server, web, and contracts coverage plus provider setup documentation.

This is intentionally Pi-only. Unlike #2748, which combines Hermes and Pi through ACP, this implementation follows the native RPC direction described in #402.

Why

#402 asks for Pi to participate in the existing provider/orchestration model without a Pi-specific frontend path, static fallback models, or unsafe partially initialized sessions. Pi's RPC mode provides the required session and event primitives while keeping Pi-specific behavior inside its driver, provider, adapter, and transport layers.

UI Changes

Verified in an isolated local app:

• Pi appears in provider settings and the add-provider-instance flow.
• Enabling Pi discovers the installed runtime and reports authenticated status.
• Pi exposed 46 dynamically discovered models in the tested environment.
• The text-generation model picker includes a Pi provider rail and Pi models.

Screenshots or a short recording will be attached before marking this draft ready for review.

Verification

• pnpm install --frozen-lockfile
• pnpm exec vp test run against 10 affected test files: 168 tests passed
• pnpm exec vp run --filter t3 --filter @t3tools/web --filter @t3tools/contracts typecheck
• Targeted vp lint for changed TypeScript/JavaScript files
• Targeted vp fmt --check for changed source and documentation files
• git diff --check origin/main...HEAD
• Isolated paired-browser verification of Pi settings, discovery, provider-instance selection, and model selection

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

The implementation is focused to one provider, but it necessarily spans contracts, server runtime, web registration, tests, and documentation. This remains a draft while maintainers advise whether they prefer this as one vertical PR or a staged series.

Note

Add Pi provider integration via RPC with session management, text generation, and approval gating

• Adds a full Pi provider driver backed by the @earendil-works/pi-coding-agent package, wiring it into the built-in provider registry alongside existing providers.
• Implements PiRpcClient — a process-spawned JSONL transport with correlated request/response handling, streaming stdout classification, timeout management, and process lifecycle control.
• Implements PiAdapter for session/turn lifecycle, assistant content and reasoning streaming, tool approval gating via an injected extension (t3-approvals.ts), and user input round-trips.
• Implements PiTextGeneration for commit messages, PR content, branch names, and thread titles using structured JSON output with schema validation and output sanitization.
• Adds PiProvider status probing via pi --version and live model discovery via RPC; adds Pi settings schema to contracts and registers the provider in the web UI with an 'Early Access' badge.
• Risk: Pi models are discovered dynamically at runtime with no static default; missing binary or empty model list degrades to a warning/unknown auth snapshot rather than an error.

📊 Macroscope summarized f8389d5. 20 files reviewed, 0 issues evaluated, 0 issues filtered, 0 comments posted

🗂️ Filtered Issues

No issues evaluated.

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[macroscopeapp]

Effect Service Conventions: one issue found. PiTextGeneration.ts recovers a known tagged failure with Effect.catchTag, which the conventions disallow (and which diverges from every sibling text-generation implementation that uses Effect.catchTags).

^{Posted via Macroscope — Effect Service Conventions}

[juliusmarminge]

we're not adding providers right now. we'll reconsider this after our new orchestrator has shipped #2829