docs: system_prompt limit is 4,000 tokens (2,000 recommended)

[Him188]

Summary

Companion to fishaudio/platform-api#1296 — prompt budgets are now measured in tokens:

• Quickstart and Build/Configuration: cap is 4,000 tokens with ≤2,000 recommended (Builder no longer hard-stops input at 4,000 chars).
• Authenticated sessions: overrides system_prompt is 4,000 tokens, same budget as the configured prompt (was 8,000 characters).
• Agent errors: 422 example rewritten to the real value_error shape emitted by the token validator (verified against the actual model output).

first_message/first_message_prompt (10,000 chars) and the analysis prompt (1,000 chars) are unchanged.

🤖 Generated with Claude Code

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Summary by CodeRabbit

• Documentation
  • Updated system prompt limits from 4,000 characters to 4,000 tokens across configuration, authentication, and quickstart guidance.
  • Added a recommendation to keep prompts under 2,000 tokens to help reduce latency and costs.
  • Updated validation error examples to reflect token-based limit enforcement.

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Project	Status	Preview	Updated (UTC)
hanabiaiinc	🔴 Failed	–	Aug 9, 2026, 6:43 AM

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Review failed

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c1b92e71-3ddf-497d-a694-9384d3bddbd1

📥 Commits

Reviewing files that changed from the base of the PR and between 2e68889 and c4fbf09.

📒 Files selected for processing (4)

• agents/build/configuration.mdx
• agents/deploy/authenticated-sessions.mdx
• agents/quickstart.mdx
• api-reference/agent-errors.mdx

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📝 Walkthrough

Walkthrough

The documentation changes replace character-based system prompt limits with a 4,000-token limit. They add a 2,000-token recommendation and update the 422 validation error example.

Changes

System prompt token limits

Layer / File(s)	Summary
Token limit guidance and validation example agents/build/configuration.mdx, agents/deploy/authenticated-sessions.mdx, agents/quickstart.mdx, api-reference/agent-errors.mdx	The documentation now states a 4,000-token system prompt limit, recommends staying below 2,000 tokens in applicable guides, and shows the revised token-limit validation error.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• fishaudio/docs#116: Updates the same agent documentation pages and introduces related limit and validation examples.
• fishaudio/docs#119: Updates prompt-related documentation across the same files.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/system-prompt-token-limit

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