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Michael Suchacz
8eb1e43f0b
## Problem
Selecting a reasoning effort on a Google (Gemini) chat model either got
dropped or broke the request outright, and even when the request
succeeded, Gemini chats never showed thinking blocks:
- The native `fantasygoogle` path had no case in `applyReasoningEffort`
at all, so effort was silently ignored. With only `include_thoughts`
configured, Gemini 3+ models default to no thinking, so chats produced
zero reasoning tokens.
- The path chat generation actually uses today routes Google providers
through aibridge as openai-compat clients and forwarded the raw effort
string as `reasoning_effort`. Google's OpenAI-compatible endpoint
validates that value against the model's supported thinking levels
instead of clamping, so out-of-range efforts fail the whole request with
HTTP 400. Verified against the live Gemini API: `gemini-3.1-pro-preview`
accepts low/medium/high and rejects none/minimal/xhigh/max. Because the
config's default effort is sent whenever the user selects nothing, a
config whose default falls outside the model's supported set failed
every no-selection message.
- Google's OpenAI-compatible endpoint never emits thought text for
`reasoning_effort` requests. Thoughts require
`extra_body.google.thinking_config` with `include_thoughts`, which is
mutually exclusive with `reasoning_effort`, and even then the thought
deltas come back inline in `content` (marked
`extra_content.google.thought`, wrapped in `<thought>` markers) rather
than in the `reasoning_content` field OpenAI-compatible clients parse.
So no reasoning parts were ever produced, persisted, or rendered for
Gemini chats (verified live in UAT).
## Fix
Reasoning effort:
- Map the global reasoning effort scale onto Google's `thinking_level`
in `applyReasoningEffort`, gated to Gemini 3+ models and clamped to each
model's supported subset (3.0 Pro launched with LOW/HIGH only, 3.1 Pro
added MEDIUM, Flash accepts all four through 3.6 while 3.7 and the
latest flash aliases drop MINIMAL, image models accept HIGH plus MINIMAL
for flash). Pre-Gemini-3 models reject `thinking_level`, so effort
degrades to a no-op for them and a config-pinned level is dropped at
call time instead of failing every generation.
- Add `thinking_level` to `ChatModelGoogleThinkingConfig` so admins can
pin a level for configs without user-selectable effort. A resolved
per-turn effort overrides the pinned level; an explicit
`thinking_budget` wins over both since the Google API rejects requests
that set `thinking_budget` and `thinking_level` together, and config
validation now rejects that combination up front. The admin panel picks
up the new field automatically through the generated model-options
schema.
Thinking blocks on the openai-compat path (the path chat generation
uses), translated in both directions at the existing Gemini transport
seam:
- chatd's OpenAI-compat request patch swaps `reasoning_effort` for an
equivalent `extra_body.google.thinking_config` with `include_thoughts`
enabled: `thinking_level` on Gemini 3+ (clamped to the model's supported
subset), `thinking_budget` on earlier models (effort `none` maps to
budget 0, which disables thinking). Non-Gemini models and non-Google
routes are untouched.
- The same transport rewrites Google's responses so thought output
surfaces as `reasoning_content`, which fantasy already converts into
reasoning parts: streaming bodies are rewritten per SSE line (preserving
streaming latency), JSON bodies in place, with the
`<thought>`/`</thought>` markers stripped at the transitions.
- aibridge's chat-completions interception preserves the `extra_body`
passthrough that openai-go's typed params silently drop, forwarding it
to Google upstreams only, so the chatd -> aibridge -> Google route
carries the thinking config end to end.
## Validation
- `go test ./coderd/x/chatd/... ./aibridge/... ./internal/googleopenai
./codersdk` pass; golangci-lint clean on touched packages.
- New unit tests cover the effort-to-level mapping for every effort
value, per-model clamping on both paths, the effort-to-thinking_config
request swap (level, budget, pinned-config precedence, non-Gemini
passthrough), SSE and JSON thought-response rewriting (fixtures mirror
live captures, including tool-call and no-thought streams), an
end-to-end fake-SSE test through the fantasy pipeline proving reasoning
deltas emerge with markers stripped, and aibridge `extra_body`
preservation (including proof the typed round trip drops it).
- Verified live against `generativelanguage.googleapis.com` on
`gemini-3-flash-preview` and `gemini-2.5-flash` through the real
chatprovider stack: reasoning deltas stream through with markers
stripped and answer text intact.
- Live UAT on a dogfood deployment (remote Coder Agents chat, 4 rounds):
effort clamping verified end to end (rounds 1-2), the missing-thoughts
limitation isolated (round 3), and the fix validated (round 4):
expandable, readable thinking blocks render for
`gemini-3.1-pro-preview`, `gemini-3-flash-preview`, and
`gemini-2.5-flash` at effort=high; no `<thought>` marker leaks;
effort=none produces no block and no 400; multi-turn history replay
works with a thinking block on each turn.
- `make gen` regenerated `typesGenerated.ts` and
`chatModelOptionsGenerated.json`; `pnpm -C site lint:types` passes.
> 🤖 Mux acted on Mike's behalf to create this pull request.
<!-- mux-attribution: model=claude-opus-4-6 thinking=high -->