docs: document selectable custom inference endpoint API formats

[hongyi-chen]

What

Updates agents/inference/custom-inference-endpoint.mdx for the API-format selector: adds a
Supported API formats section, a configuration step for choosing the format, and reworks the
frontmatter, key features, and comparison table that all claimed OpenAI Chat Completions was the
only supported surface.

Why

Flagged by the missing_docs changelog cross-check (2026.07.31: "Custom model endpoints can now
select an OpenAI Chat Completions, OpenAI Responses, or Anthropic Messages ..."). The changelog
mention was the only coverage.

Source of truth

• crates/ai/src/api_keys.rs — CustomEndpointSchema (OpenaiChatCompletions as the default,
  OpenaiResponses, AnthropicMessages) and its display names.
• app/src/settings_view/custom_inference_modal.rs — the schema dropdown in the endpoint modal.
• app/src/settings_view/ai_page.rs — the settings copy listing the three formats.

Deferred findings from this run

Nothing from the audit was silently dropped. The full deferral list lives in the companion
bookkeeping PR (docs/missing-docs-audit-bookkeeping); in summary:

• 15 warp-server public API routes missing from the OpenAPI spec — routed to the
  sync-openapi-spec skill rather than hand-written, per the skill's public/private guardrail.
• 32 terminology/staleness findings — owned by the style_lint skill.
• 1 new server-side agent tool (report_external_reference) — reached only through the hidden
  oz harness-support CLI, so no public surface to document yet.

---

Conversation: https://staging.warp.dev/conversation/c45bb2ea-d33b-4723-8249-478547f81a47
Run: https://oz.staging.warp.dev/runs/019fc891-7c04-779b-b006-328169d8a0d7

This PR was generated with Oz.

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Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview	Aug 3, 2026 5:21pm

[hongyi-chen]

Heads-up on overlap: #438 also documents the custom inference endpoint API schema selector, but both of its files are under src/content/docs/agent-platform/inference/, a path that no longer exists after the agent-platform/ → agents/ rename in #420. This PR targets the current path. #438 additionally touches bring-your-own-api-key.mdx, which this PR does not — worth checking whether that part is still needed before closing either one.

[hongyi-chen]

Reviewer routing: scripts/suggest_reviewers.py resolves the source file behind this change to the @warpdotdev/oss-maintainers team (matched via the root / rule in the warp repo's .github/STAKEHOLDERS). Requesting that team as a reviewer didn't take through the API from this run, so it needs assigning manually.