fix(ai-providers): read the system prompt and tools from the Pi 0.86+ transcript - #620

Problem

Closes #619.

Pi 0.86.0 changed a custom provider's stream input from Context to a normalized TranscriptContext: the system prompt and tool declarations are folded into a leading transcript system message, and later system messages carry prompt/tool deltas. The Antigravity adapter still read context.systemPrompt / context.tools, so that leading system message fell through to the tool-result branch and became a functionResponse with no name:

GenerateContentRequest.contents[0].parts[0].function_response.name: Name cannot be empty.

Every request on Pi 0.86+ failed, and independently of the 400 the system prompt and all tool declarations were dropped. Cursor read the same two fields and silently fell back to its generic chat-only prompt with no tools.

Value

google-antigravity works again on Pi 0.86+ while the declared Pi 0.85.1 baseline keeps working unchanged, and the failure class is closed at the shared cause rather than per provider.

Approach

• New extensions/ai-providers/transcript.ts: replays transcript system messages into the prompt and tool set currently in effect, mirroring Pi's getCurrentSystemPrompt / getCurrentTools without importing helpers that do not exist before Pi 0.86. applyTranscript returns the old Context untouched, so Pi <= 0.85.1 behavior is preserved exactly.
• Antigravity buildRequestBody resolves the transcript once; convertMessages receives conversation messages only; buildTools takes the resolved tool list.
• Google converter: only assistant turns are rewritten, and non-conversation roles or nameless tool results no longer become a functionResponse.
• Cursor: buildCursorRequest / streamCursor resolve the transcript at the entry point.
• No dependency, lockfile, or peer-range change — this lands independently of the baseline discussion in chore(deps): define and enforce the supported Pi baseline #328.

Validation

• Differential against Pi 0.87.1's own replay (getCurrentSystemPrompt / getCurrentTools) across five message sets — leading system message; later section patch with toolsRemoved / toolsAdded; content plus sections; two system messages; no system message. Prompt text and tool set are identical in all five.
• tests/extensions/ai-providers/antigravity.test.ts 58/58 and cursor.test.ts 36/36 (94 total on the current head). The four new regression tests fail when the provider changes are stashed, so they pin the regression rather than the implementation.
• Cursor local HTTP/2 handshake regression covers both legacy Context and Pi 0.86+ transcript input. Assertions inspect the actual requestContextResult: patched/deleted prompt sections, the final tool names/descriptions/schemas after additions/removals, and the openpi provider identifier.
• Previously completed real-account validation on Pi 0.87.1 (not rerun for the test-only follow-up), extension loaded with -ne -ns -np -nc --no-session -e extensions/ai-providers/index.ts:
  • control (unpatched npm @tt-a1i/openpi@0.8.1): the exact 400 from bug(antigravity): Pi 0.86+ 下 provider stream 收到 TranscriptContext，每次请求都以 400 失败 #619;
  • patched: gemini-3.8-flash-high plain reply, read tool round trip, and claude-sonnet-4-6 read tool round trip.
• Latest bun run test: Node tests 1889 passed / 0 failed / 5 skipped; Vitest 275 tests passed, but tests/web/app-render.spec.ts could not load because @xterm/addon-fit is missing. The overall command is not green.
• bun run check: config/docs/discipline checks pass; check:web stops on missing @xterm/addon-fit / @xterm/xterm and related type errors. Changed-file Biome format/lint and git diff --check pass. tsc --noEmit still reports the same 20 environment errors involving node-pty / @xterm/*, with no errors in the changed test file.

Impact

• Fixes the antigravity 400 and restores prompt/tool delivery on Pi 0.86+; no wire-format change for Pi <= 0.85.1.
• Touches extensions/ai-providers/antigravity/google-conversion.ts, which fix(antigravity): preserve local schema refs #488 also modifies; this branch is based on 43cd2e9 and does not include fix(antigravity): preserve local schema refs #488.
• Not verified: a real Cursor account turn; Cursor coverage is automated, including the local HTTP/2 request-context handshake, not live-service acceptance.
• Does not move the peer range or lockfile. Whether the supported baseline should become >= 0.86 stays with chore(deps): define and enforce the supported Pi baseline #328.