fix(agent): raise combined system prompt cap to 1 MiB#1252
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The session/new handler rejects combined system prompts (harness prompt + persona + discovered AGENTS.md/skill hints) over MAX_SYSTEM_PROMPT_BYTES. At 512 KiB this falsely rejects sessions when a machine has a large skill library: buzz-agent inlines the full body of every SKILL.md found under ~/.agents/skills (and .goose/.claude skills + AGENTS.md), so a user with ~76 skills hits 'combined system prompt exceeds 512KB limit (533647 bytes)' and the agent cannot start a session. Raise MAX_SYSTEM_PROMPT_BYTES from 512 KiB to 1 MiB, matching the sibling MAX_PROMPT_BYTES. The cap is local to the buzz-acp<->buzz-agent stdio boundary, not the relay frame size, so this does not affect wire limits. Update the oversized-prompt integration test accordingly. Amp-Thread-ID: https://ampcode.com/threads/T-019efb67-0076-766e-be17-f563c0e12e01 Co-authored-by: Amp <amp@ampcode.com>
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Problem
buzz-agent'ssession/newhandler rejects any combined system prompt (harness prompt + persona + discoveredAGENTS.md/skill hints) larger thanMAX_SYSTEM_PROMPT_BYTES(512 KiB). The hints builder incrates/buzz-agent/src/hints.rsinlines the full body of everySKILL.mdit discovers under~/.agents/skills(plus.goose/skills,.claude/skills, andAGENTS.mdlayers).On a machine with a large personal skill library this overflows the cap. A user with ~76 skills (~517 KiB of
SKILL.mdbodies) hits:and the agent (e.g. Fizz on the Block staging relay) can't start a session at all.
Change
Raise
MAX_SYSTEM_PROMPT_BYTESfrom 512 KiB to 1 MiB, matching the siblingMAX_PROMPT_BYTESconstant in the same file.This cap guards the
buzz-acp↔buzz-agentstdio (ACP) boundary; it is not the relay frame size (BUZZ_MAX_FRAME_BYTES/DEFAULT_MAX_FRAME_BYTES), so wire limits are unaffected.Tests
Updated
session_new_rejects_oversized_system_promptincrates/buzz-agent/tests/fake_llm.rsto use a 1100 KiB payload and assert the new1024KB limitmessage.cargo test -p buzz-agentpasses (21 unit + integration tests).Notes
session/new. A follow-up could summarize/elide skill bodies or make the cap env-tunable (likeBUZZ_AGENT_MAX_TOOL_RESULT_TEXT_BYTES), but that's out of scope here.