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feat: forward generation params via MITM + add usageMetadata to Gemini

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- Add GenerationParams struct to MitmStore for temperature, top_p,
  top_k, max_output_tokens, stop_sequences, frequency/presence_penalty
- MITM modify_request injects params into request.generationConfig
- All 3 endpoints (Completions, Responses, Gemini) store client params
- Add usageMetadata to Gemini sync responses (promptTokenCount,
  candidatesTokenCount, totalTokenCount, thoughtsTokenCount)
- Add generation param fields to GeminiRequest (temperature, topP, etc.)
- Completions stream_options.include_usage emits final usage chunk
- Completions reasoning_tokens in completion_tokens_details
- Update endpoint gap analysis doc (all high-priority gaps resolved)
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Nikketryhard
2026-02-15 14:23:05 -06:00
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# Endpoint Gap Analysis
> **Generated:** 2026-02-15 (updated)
> **Proxy Version:** 3.1.0
> **Scope:** All three API endpoints vs official OpenAI / Gemini specifications
---
## Table of Contents
- [Endpoint Overview](#endpoint-overview)
- [Feature Parity Matrix](#feature-parity-matrix)
- [Detailed Endpoint Analysis](#detailed-endpoint-analysis)
- [Responses API (`/v1/responses`)](#responses-api-v1responses)
- [Chat Completions API (`/v1/chat/completions`)](#chat-completions-api-v1chatcompletions)
- [Gemini API (`/v1/gemini`)](#gemini-api-v1gemini)
- [Priority Gaps](#priority-gaps)
- [Architecture Notes](#architecture-notes)
---
## Endpoint Overview
The proxy exposes three main API endpoints, each serving different client ecosystems:
| Endpoint | Protocol | Primary Clients | Spec Reference |
| --------------------------- | --------------------------- | ----------------------------------------------------- | ------------------------------------------------------------------------------------------------------------ |
| `POST /v1/responses` | OpenAI Responses API | Claude Code, Antigravity-native clients | [platform.openai.com/docs/api-reference/responses](https://platform.openai.com/docs/api-reference/responses) |
| `POST /v1/chat/completions` | OpenAI Chat Completions API | OpenCode, Vercel AI SDK, any OpenAI-compatible client | [platform.openai.com/docs/api-reference/chat](https://platform.openai.com/docs/api-reference/chat/create) |
| `POST /v1/gemini` | Custom Gemini-native API | Direct Gemini-format consumers | [ai.google.dev/api](https://ai.google.dev/api) (loosely based) |
All three endpoints share the same backend pipeline:
```
Client Request → Proxy Endpoint → LS (Language Server) → Google API
↓
MITM Proxy (captures real usage + injects generation params + tool calls)
```
---
## Feature Parity Matrix
### Core Features
| Feature | Responses | Completions | Gemini |
| -------------------- | :-------: | :---------: | :----: |
| Sync mode | ✅ | ✅ | ✅ |
| Streaming mode (SSE) | ✅ | ✅ | ✅ |
| Model selection | ✅ | ✅ | ✅ |
| Model validation | ✅ | ✅ | ✅ |
| Auth check (OAuth) | ✅ | ✅ | ✅ |
| Timeout control | ✅ | ✅ | ✅ |
### Generation Parameters (MITM-injected)
| Feature | Responses | Completions | Gemini |
| ------------------- | :-------: | :---------: | :----: |
| `temperature` | ✅ | ✅ | ✅ |
| `top_p` / `topP` | ✅ | ✅ | ✅ |
| `top_k` / `topK` | ❌ | ❌ | ✅ |
| `max_output_tokens` | ✅ | ✅ | ✅ |
| `stop_sequences` | ❌ | ❌ | ✅ |
| `frequency_penalty` | ❌ | ✅ | ❌ |
| `presence_penalty` | ❌ | ✅ | ❌ |
> **Note:** All generation parameters are forwarded to Google's API via MITM injection into `request.generationConfig`. They override the LS defaults.
### Thinking / Reasoning
| Feature | Responses | Completions | Gemini |
| ---------------------------------- | :-------------------------------: | :-------------------------------: | :---------------------: |
| Thinking — LS path (streaming) | ✅ `reasoning_summary_text.delta` | ✅ `reasoning_content` delta | ✅ `thought: true` part |
| Thinking — LS path (sync) | ✅ `reasoning` output item | ✅ `reasoning_content` in message | ✅ `thought: true` part |
| Thinking — Bypass path (streaming) | ✅ | ✅ | ✅ |
| Thinking — Bypass path (sync) | ✅ | ✅ | ✅ |
| Thinking signature (multi-turn) | ✅ `thinking_signature` field | ❌ Not applicable | ❌ Not applicable |
### Tool Calls
| Feature | Responses | Completions | Gemini |
| ---------------------------- | :-----------------------------: | :------------------------: | :-------------------------------------: |
| Tool definitions input | ✅ OpenAI format → Gemini | ✅ OpenAI format → Gemini | ✅ Native Gemini format |
| Tool choice control | ✅ `tool_choice` | ✅ `tool_choice` | ✅ `tool_config` |
| Tool call output (streaming) | ✅ `function_call` items | ✅ `tool_calls` in delta | ✅ `functionCall` parts |
| Tool call output (sync) | ✅ `function_call` items | ✅ `tool_calls` in message | ✅ `functionCall` parts |
| Tool result input | ✅ `function_call_output` items | ✅ `tool` role messages | ✅ `functionResponse` in `tool_results` |
| MITM bypass (custom tools) | ✅ | ✅ | ✅ |
| Stale state protection | ✅ | ✅ | ✅ |
### Session Management
| Feature | Responses | Completions | Gemini |
| ------------------------------------ | :---------------------: | :--------------: | :---------------------: |
| Session/conversation reuse | ✅ `conversation` field | ❌ Not supported | ✅ `conversation` field |
| Session listing (`GET /v1/sessions`) | ✅ Shared | ✅ Shared | ✅ Shared |
| Session deletion | ✅ Shared | ✅ Shared | ✅ Shared |
### Usage / Token Tracking
| Feature | Responses | Completions | Gemini |
| -------------------------------- | :---------------------------: | :-------------------------------: | :--------------------------: |
| Usage in sync response | ✅ MITM real tokens | ✅ MITM real tokens | ✅ `usageMetadata` |
| Usage in streaming (final chunk) | ❌ Not emitted | ✅ `stream_options.include_usage` | ❌ Not emitted |
| `reasoning_tokens` in usage | ✅ In `output_tokens_details` | ✅ In `completion_tokens_details` | ✅ `thoughtsTokenCount` |
| Cache tokens | ✅ `cached_tokens` | ✅ `cached_tokens` | ✅ `cachedContentTokenCount` |
---
## Detailed Endpoint Analysis
### Responses API (`/v1/responses`)
**Spec:** [OpenAI Responses API](https://platform.openai.com/docs/api-reference/responses)
#### Request Fields
| Field | Spec | Status | Implementation Details |
| ---------------------------- | ------------- | :----: | -------------------------------------------------------------------------------------------------------------------------------- |
| `model` | Required | ✅ | Mapped to internal model enum via `lookup_model()` |
| `input` | Required | ✅ | String or array. Array supports `message` items and `function_call_output` items |
| `instructions` | Optional | ✅ | Prepended to user text as system instructions |
| `stream` | Optional | ✅ | SSE stream with `response.*` events |
| `tools` | Optional | ✅ | OpenAI function format → auto-converted to Gemini `functionDeclarations` via `openai_tools_to_gemini()` |
| `tool_choice` | Optional | ✅ | `"auto"`, `"required"`, `"none"`, or `{"type":"function","function":{"name":"X"}}` → converted to Gemini `functionCallingConfig` |
| `store` | Optional | ✅ | Accepted, echoed in response. Not actually persisted. |
| `temperature` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig` injection. |
| `top_p` | Optional | ✅ | **Forwarded** to Google via MITM. |
| `max_output_tokens` | Optional | ✅ | **Forwarded** to Google via MITM. |
| `previous_response_id` | Optional | ✅ | Accepted, echoed. Not used for chaining (use `conversation` instead). |
| `metadata` | Optional | ✅ | Accepted, echoed back in response. |
| `user` | Optional | ✅ | Accepted, echoed. |
| `conversation` | **Extension** | ✅ | Proxy-specific: session ID for multi-turn cascade reuse. |
| `timeout` | **Extension** | ✅ | Proxy-specific: request timeout in seconds (default 120). |
| `reasoning.effort` | Optional | ❌ | Could map to model variant selection (e.g., `"high"` → Opus, `"low"` → Flash). |
| `reasoning.generate_summary` | Optional | ❌ | Not implemented. Could control thinking output inclusion. |
| `truncation` | Optional | ❌ | Not applicable — LS manages context window. |
| `parallel_tool_calls` | Optional | ✅ | Hardcoded `true` in response. |
#### Response Object
| Field | Spec | Status | Notes |
| ---------------------- | ------------- | :----: | ---------------------------------------------------------------- |
| `id` | Required | ✅ | `resp_` + UUID |
| `object` | Required | ✅ | Always `"response"` |
| `created_at` | Required | ✅ | Unix timestamp |
| `status` | Required | ✅ | `"completed"` or `"incomplete"` |
| `completed_at` | Required | ✅ | Unix timestamp or null |
| `error` | Required | ✅ | null on success |
| `incomplete_details` | Required | ✅ | null |
| `instructions` | Required | ✅ | Echoed from request |
| `max_output_tokens` | Required | ✅ | Echoed or null |
| `model` | Required | ✅ | Model name string |
| `output` | Required | ✅ | Array of `reasoning` and/or `message` items |
| `parallel_tool_calls` | Required | ✅ | `true` |
| `previous_response_id` | Required | ✅ | Echoed or null |
| `reasoning` | Required | ✅ | `{effort: null, summary: null}` |
| `store` | Required | ✅ | Echoed |
| `temperature` | Required | ✅ | Echoed (default 1.0) |
| `text` | Required | ✅ | `{format: {type: "text"}}` |
| `tool_choice` | Required | ✅ | `"auto"` |
| `tools` | Required | ✅ | Echoed or `[]` |
| `top_p` | Required | ✅ | Echoed (default 1.0) |
| `truncation` | Required | ✅ | `"disabled"` |
| `usage` | Required | ✅ | MITM-intercepted real tokens when available, estimated otherwise |
| `user` | Required | ✅ | Echoed or null |
| `metadata` | Required | ✅ | Echoed or `{}` |
| `thinking_signature` | **Extension** | ✅ | Proxy-specific: opaque blob for multi-turn thinking chain |
#### Streaming Events
| Event | Spec | Status | Notes |
| ---------------------------------------- | --------- | :----: | ------------------------------ |
| `response.created` | Required | ✅ | Initial response shell |
| `response.in_progress` | Required | ✅ | |
| `response.output_item.added` | Required | ✅ | For reasoning + message items |
| `response.content_part.added` | Required | ✅ | |
| `response.output_text.delta` | Required | ✅ | Progressive text deltas |
| `response.output_text.done` | Required | ✅ | |
| `response.content_part.done` | Required | ✅ | |
| `response.output_item.done` | Required | ✅ | |
| `response.completed` | Required | ✅ | Final event with full response |
| `response.reasoning_summary_text.delta` | Required | ✅ | Progressive thinking deltas |
| `response.reasoning_summary_text.done` | Required | ✅ | |
| `response.function_call_arguments.delta` | For tools | ✅ | Tool call argument streaming |
| `response.function_call_arguments.done` | For tools | ✅ | |
---
### Chat Completions API (`/v1/chat/completions`)
**Spec:** [OpenAI Chat Completions API](https://platform.openai.com/docs/api-reference/chat/create)
#### Request Fields
| Field | Spec | Status | Implementation Details |
| ------------------------- | ------------- | :----: | -------------------------------------------------------------------- |
| `model` | Required | ✅ | Mapped to internal model enum |
| `messages` | Required | ✅ | Supports `system`, `developer`, `user`, `assistant`, `tool` roles |
| `messages[].content` | Required | ✅ | String or array of `{type: "text", text: "..."}` objects |
| `messages[].tool_calls` | Optional | ✅ | For assistant messages with tool calls |
| `messages[].tool_call_id` | Optional | ✅ | For tool result messages |
| `stream` | Optional | ✅ | SSE with `chat.completion.chunk` events |
| `stream_options` | Optional | ✅ | `include_usage: true` emits final usage chunk before `[DONE]` |
| `tools` | Optional | ✅ | OpenAI function format → auto-converted to Gemini |
| `tool_choice` | Optional | ✅ | `"auto"`, `"none"`, `"required"`, or specific function |
| `timeout` | **Extension** | ✅ | Proxy-specific (default 120s) |
| `temperature` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.temperature` |
| `top_p` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.topP` |
| `max_tokens` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.maxOutputTokens` |
| `max_completion_tokens` | Optional | ✅ | **Forwarded** (same as `max_tokens`, newer OpenAI param) |
| `frequency_penalty` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.frequencyPenalty` |
| `presence_penalty` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.presencePenalty` |
| `user` | Optional | ✅ | Accepted, not used |
| `n` | Optional | ❌ | N/A — single generation only |
| `logprobs` | Optional | ❌ | N/A |
| `top_logprobs` | Optional | ❌ | N/A |
| `logit_bias` | Optional | ❌ | N/A |
| `response_format` | Optional | ❌ | Could be useful for JSON mode |
| `seed` | Optional | ❌ | N/A |
| `stop` | Optional | ❌ | Could be forwarded as `stopSequences` |
#### Sync Response Object
| Field | Spec | Status | Notes |
| ------------------------------------------------------------ | ----------- | :----: | -------------------------------------------- |
| `id` | Required | ✅ | `chatcmpl-` + UUID |
| `object` | Required | ✅ | `"chat.completion"` |
| `created` | Required | ✅ | Unix timestamp |
| `model` | Required | ✅ | Model name |
| `choices[0].index` | Required | ✅ | `0` |
| `choices[0].message.role` | Required | ✅ | `"assistant"` |
| `choices[0].message.content` | Required | ✅ | Response text |
| `choices[0].message.reasoning_content` | Extension | ✅ | Thinking text (when model produces thinking) |
| `choices[0].message.tool_calls` | Conditional | ✅ | When model returns tool calls |
| `choices[0].message.refusal` | Optional | ❌ | Not implemented |
| `choices[0].message.annotations` | Optional | ❌ | Not implemented |
| `choices[0].logprobs` | Optional | ❌ | Not implemented |
| `choices[0].finish_reason` | Required | ✅ | `"stop"` or `"tool_calls"` |
| `usage.prompt_tokens` | Required | ✅ | MITM real or estimated |
| `usage.completion_tokens` | Required | ✅ | MITM real or estimated |
| `usage.total_tokens` | Required | ✅ | Sum |
| `usage.prompt_tokens_details.cached_tokens` | Optional | ✅ | MITM cache read tokens |
| `usage.completion_tokens_details.reasoning_tokens` | Optional | ✅ | MITM thinking token count |
| `usage.completion_tokens_details.accepted_prediction_tokens` | Optional | ❌ | N/A |
| `usage.completion_tokens_details.rejected_prediction_tokens` | Optional | ❌ | N/A |
| `system_fingerprint` | Deprecated | ❌ | Cosmetic, not needed |
| `service_tier` | Optional | ❌ | Cosmetic, not needed |
#### Streaming Chunk Object
| Field | Spec | Status | Notes |
| ------------------------------------ | --------------- | :----: | ----------------------------------------------------- |
| `id` | Required | ✅ | Same across all chunks |
| `object` | Required | ✅ | `"chat.completion.chunk"` |
| `created` | Required | ✅ | Same across all chunks |
| `model` | Required | ✅ | |
| `choices[0].index` | Required | ✅ | `0` |
| `choices[0].delta.role` | First chunk | ✅ | `"assistant"` in first chunk |
| `choices[0].delta.content` | Text chunks | ✅ | Progressive text deltas |
| `choices[0].delta.reasoning_content` | Thinking chunks | ✅ | Progressive thinking deltas |
| `choices[0].delta.tool_calls` | Tool chunks | ✅ | Tool call data |
| `choices[0].delta` | Final chunk | ✅ | Empty `{}` |
| `choices[0].finish_reason` | Final chunk | ✅ | `"stop"` or `"tool_calls"` |
| `choices[0].logprobs` | Optional | ❌ | Not implemented |
| `usage` (final chunk) | Optional | ✅ | Emitted when `stream_options.include_usage` is `true` |
| `data: [DONE]` | Required | ✅ | Stream termination signal |
---
### Gemini API (`/v1/gemini`)
**Spec:** Custom endpoint loosely based on [Gemini REST API](https://ai.google.dev/api/generate-content)
> **Note:** This is NOT a 1:1 Gemini API replica. It's a simplified proxy-native endpoint that uses Gemini's `functionDeclarations` / `functionCall` / `functionResponse` format directly, avoiding OpenAI ↔ Gemini format conversion overhead.
#### Request Fields
| Field | Spec | Status | Implementation Details |
| --------------------------------------- | -------- | :----: | --------------------------------------------------------------- |
| `model` | Required | ✅ | Mapped to internal model enum |
| `input` | Required | ✅ | String only (no array/multipart) |
| `tools` | Optional | ✅ | Native Gemini `[{functionDeclarations: [...]}]` format |
| `tool_config` | Optional | ✅ | Native Gemini `{functionCallingConfig: {mode: "AUTO"}}` |
| `tool_results` | Optional | ✅ | Array of `{functionResponse: {name, response}}` |
| `conversation` | Optional | ✅ | Session ID for cascade reuse |
| `stream` | Optional | ✅ | SSE streaming |
| `timeout` | Optional | ✅ | Default 120s |
| `temperature` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.temperature` |
| `top_p` / `topP` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.topP` |
| `top_k` / `topK` | Optional | ✅ | **Forwarded** to Google via MITM `generationConfig.topK` |
| `max_output_tokens` / `maxOutputTokens` | Optional | ✅ | **Forwarded** via MITM `generationConfig.maxOutputTokens` |
| `stop_sequences` / `stopSequences` | Optional | ✅ | **Forwarded** via MITM `generationConfig.stopSequences` |
#### Sync Response Object
| Field | Spec | Status | Notes |
| -------------------------------------------- | --------- | :----: | -------------------------------- |
| `candidates[0].content.parts` | Required | ✅ | Array of text/functionCall parts |
| `candidates[0].content.parts[].text` | Text | ✅ | Response text |
| `candidates[0].content.parts[].thought` | Extension | ✅ | `true` for thinking parts |
| `candidates[0].content.parts[].functionCall` | Tool call | ✅ | `{name, args}` |
| `candidates[0].content.role` | Required | ✅ | `"model"` |
| `candidates[0].finishReason` | Required | ✅ | `"STOP"` |
| `modelVersion` | Required | ✅ | Model name string |
| `usageMetadata` | Optional | ✅ | MITM-intercepted token counts |
`usageMetadata` fields:
| Field | Status | Notes |
| ------------------------- | :----: | ------------------------- |
| `promptTokenCount` | ✅ | Input tokens |
| `candidatesTokenCount` | ✅ | Output tokens |
| `totalTokenCount` | ✅ | Input + output |
| `thoughtsTokenCount` | ✅ | Thinking/reasoning tokens |
| `cachedContentTokenCount` | ✅ | Cache read tokens |
#### Streaming Format
Each SSE `data:` chunk is a complete Gemini-format JSON object with progressive `candidates[0].content.parts`:
```
data: {"candidates":[{"content":{"parts":[{"text":"thinking...","thought":true}],"role":"model"}}],"modelVersion":"opus-4.6"}
data: {"candidates":[{"content":{"parts":[{"text":"Hello!"}],"role":"model"}}],"modelVersion":"opus-4.6"}
data: {"candidates":[{"content":{"parts":[{"text":""}],"role":"model"},"finishReason":"STOP"}],"modelVersion":"opus-4.6"}
data: [DONE]
```
---
## Priority Gaps
### 🔴 High Priority — RESOLVED ✅
All high-priority gaps have been addressed:
1. ~~**Completions: `stream_options.include_usage`**~~ → ✅ Implemented
2. ~~**Completions: `completion_tokens_details.reasoning_tokens`**~~ → ✅ Implemented
3. ~~**Completions: Accept `temperature`, `top_p`, `max_tokens`**~~ → ✅ Forwarded via MITM
4. ~~**Gemini: `usageMetadata`**~~ → ✅ Implemented
### 🟡 Medium Priority
5. **Responses: `reasoning.effort`**
- **What:** Map reasoning effort levels (`"high"`, `"medium"`, `"low"`) to model variant selection
- **Why:** Could automatically select Opus vs Flash based on reasoning needs
- **Effort:** Medium — needs model selection logic changes
6. **Completions: Session/conversation support**
- **What:** Add session reuse similar to Responses and Gemini endpoints
- **Why:** Would allow multi-turn conversations via the completions API
- **Effort:** Medium — need a way to pass session ID (maybe via `user` field or custom header)
7. **Completions: `stop` sequences**
- **What:** Forward `stop` to Google as `stopSequences` in `generationConfig`
- **Why:** Some clients use stop sequences to control generation
- **Effort:** Trivial — just add to `CompletionRequest` and `GenerationParams`
8. **Completions: `response_format` (JSON mode)**
- **What:** Forward `response_format: {"type": "json_object"}` to Google's `responseMimeType`
- **Why:** Useful for structured output
- **Effort:** Low — inject `responseMimeType: "application/json"` in generationConfig
### 🟢 Low Priority
Cosmetic or not applicable to our architecture:
9. **`system_fingerprint`** — OpenAI-specific field, meaningless for our proxy
10. **`service_tier`** — OpenAI billing concept, not applicable
11. **`n` > 1** — Multiple completions per request; our backend only generates one
12. **`logprobs`** — Would require token-level access we don't have
13. **`seed`** — Deterministic sampling not controllable through our proxy
---
## Architecture Notes
### Generation Parameter Injection
Client-specified sampling parameters are forwarded to Google's API via the MITM request modification pipeline:
```
Client sends temperature=0.5 → API handler stores in MitmStore.generation_params
↓
LS sends request to Google API
↓
MITM intercepts request
↓
modify_request() reads generation_params
↓
Injects into request.generationConfig:
temperature, topP, topK, maxOutputTokens,
stopSequences, frequencyPenalty, presencePenalty
↓
Forwards modified request to Google
```
This approach overrides whatever defaults the LS sets, giving clients direct control over sampling parameters.
### Dual Path Architecture
All three endpoints share a dual-path architecture:
```
┌─────────────────┐
│ Has custom │
Request ────────────► │ tools? │
└────────┬────────┘
│
┌──── Yes ──┴── No ────┐
│ │
┌─────▼─────┐ ┌─────▼─────┐
│ MITM │ │ LS Steps │
│ Bypass │ │ Polling │
│ Path │ │ Path │
└─────┬─────┘ └─────┬─────┘
│ │
┌─────▼─────┐ ┌─────▼─────┐
│ Poll │ │ Poll │
│ MitmStore │ │ get_steps │
│ directly │ │ from LS │
└─────┬─────┘ └─────┬─────┘
│ │
└──────────┬────────────┘
│
┌─────▼─────┐
│ Response │
│ to client │
└───────────┘
```
- **Bypass Path:** When custom tools are present, the handler polls `MitmStore` directly for response text, thinking text, and function calls. The MITM proxy captures these from the Google API response before the LS processes them.
- **LS Path:** When no custom tools are present, the handler polls the LS's `get_steps` API for progressive response data (text, thinking, status).
### Stale State Protection
All bypass paths include protection against stale `response_complete` flags from previous requests:
```rust
if complete && text.is_empty() && thinking.is_none() {
warn!("stale response_complete detected — clearing");
state.mitm_store.clear_response_async().await;
continue; // or retry
}
```
This handles the race condition where a previous request's MITM handler calls `mark_response_complete()` after the new request has already called `clear_response_async()`.
### Tool Format Conversion
```
OpenAI tools ──► openai_tools_to_gemini() ──► Gemini functionDeclarations
│
MitmStore.set_tools()
│
MITM proxy injects into
outgoing LS request
```
The Gemini endpoint skips this conversion entirely — tools are stored in native Gemini format.