GeezerVison

Moves the fantasy pin to the tip of coder_2_33 (85ffbbe). That commit is coder/fantasy#72, which merges 87 upstream charmbracelet/fantasy commits, v0.40.0 to v0.45.5. Between the two pins 117 files change. Upstream's own v0.40.0 to v0.45.5 change, without tests, testdata, examples, go.sum and the kronk provider, is 43 files, +2271/−928.

What reaches chatd

chatd builds only the anthropic, openai and openaicompat fantasy clients (chatprovider.ModelFromConfig); other vendors reach it through the AI Gateway on one of those. So the upstream changes to the Google, Vercel, OpenRouter, Bedrock, Azure and kronk providers, and to the fantasy.Agent loop and its retries, do not run in chatd. These do:

• Chat Completions and openaicompat streams keep reasoning on batched and DeepSeek-shaped chunks, keep finish_reason: length when tool calls are truncated, and stop sending empty reasoning fields. openaicompat drops assistant turns that hold only reasoning.
• Token usage. When an OpenAI-shaped backend reports reasoning tokens apart from completion tokens (reasoning larger than output), output tokens now include them, so that backend's reported output tokens and cost rise. OpenAI's own shape, where reasoning is a subset, is unchanged.
• Responses. A content-filtered turn no longer reads as a tool-call turn.
• Context overflow. Baseten, Fireworks and Parasail prompt-length errors set ContextTooLargeErr, which compaction acts on.
• Anthropic. Tool calls whose content block never closes are reported. For Claude 5 models, thinking defaults to display: "summarized" when the chat config sets none; a configured display still wins. TestThinkingDropBlockModel_RetriesWithEffort now expects the field in the retry body.
• Anthropic keepalives. Fantasy forwards message_start, message_delta and unknown events as content-free keepalive parts. The first one arrives before any model output, so this PR makes ttft_seconds and the time_to_first_token stage skip them, as they skip warnings. They still reset the stream silence guard. processStepStream ignores them, and the debug recorder counts them in its part count but records no content.
• Tool-result media now goes through upstream's shared ToolRunBuffer, which replaces fix(providers): keep tool batches ahead of media messages fantasy#64 and does the same thing.

#72 keeps coder's anthropic-sdk-go and openai-go forks, Go 1.26 and kronk v1.31.5, so upstream's SDK and Go moves do not come along.

go mod tidy raises the modules fantasy v0.45.5 requires, among them otel exporters v1.47, the AWS SDK, google.golang.org/api v0.307 and go-openapi v1. All are upgrades.

The go.mod comment now names #72 as the upstream sync.

#29861 stacks on this PR to pin coder/fantasy#62.

🤖 This PR was created with the help of Coder Agents, and will be reviewed by a human. 🏂🏻