Docs: clarify whether fast mode propagates to subagents, Workflow agents, and /code-review

What's unclear

Fast mode (/fast / "fastMode": true, Opus 4.8/4.7 only) is documented as a session-level toggle, but the docs never say whether it propagates to the other places a session spawns model requests:

1. Subagents (Task/Agent tool) — the subagents docs say built-in agents "inherit from the main conversation" for model selection, but don't say whether the fast-mode serving option rides along with that inheritance.
2. Workflow-tool agents — the workflows docs cover model selection (session model unless overridden per-stage or via CLAUDE_CODE_SUBAGENT_MODEL) but never mention fast mode.
3. /code-review — the code-review docs don't mention fast mode for the local review agents either.

The fast-mode page mentions none of these surfaces, and none of those pages mention fast mode — so a user who toggles /fast and then kicks off a multi-agent review or workflow has no way to know whether the (majority) subagent token spend is billed and served at fast-mode rates or normal rates.

Why it matters

• Cost: fast mode is billed at a higher per-token rate. In agent-heavy usage, subagents are most of the spend — whether they're fast-mode or not can dominate the bill either way. Users can't predict cost without knowing the inheritance rule.
• Latency expectations: the whole point of toggling /fast before a big fan-out is making the fan-out faster. If inheritance doesn't happen, that's an invisible no-op.
• No per-agent control either way: there's no documented fast field in agent frontmatter, no fast-variant model string, and no per-call option on the Agent/Workflow tools — so the session toggle is the only knob, which makes its scope the entire story.

Ask

Document, on the fast-mode page (and cross-referenced from the subagents/workflows pages):

1. Whether fast mode applies to subagent and workflow-agent requests when the session model is an eligible Opus (and what happens for agents that override to a non-eligible model — presumably silently normal-speed, but say so).
2. Whether /code-review's local agents run fast when the session is in fast mode.
3. If inheritance is intentional either way, whether a per-agent override is planned or out of scope.

Docs pages involved:

• https://code.claude.com/docs/en/fast-mode
• https://code.claude.com/docs/en/sub-agents
• https://code.claude.com/docs/en/workflows
• https://code.claude.com/docs/en/code-review

Environment

• Claude Code 2.1.217, macOS (darwin 25.5.0)
• Model: Opus 4.8 (fast-mode eligible)