refactor(agent): typed codes for Agent.continue precondition failures

[snimu]

Follow-up to #1583, which classified Agent.continue() precondition failures by error message text (includes("already processing"), includes("continue from")) — flagged in review as brittle: a rewording in packages/agent silently breaks the classification, and the failure mode is the bad one (a benign nothing-to-continue race would start rejecting headless idle waiters).

Linear: ENG-5407 — https://linear.app/primeintellect/issue/ENG-5407/typed-error-codes-for-agentcontinue-precondition-failures

Change

• Agent.continue() throws AgentContinueError with a stable code at its three precondition sites: busy (a run is active — retryable) and nothing-to-continue (no messages, or trailing assistant message — the turn already completed).
• The post-compaction classifier in agent-session switches on the code: busy → reschedule, nothing-to-continue → settle clean, anything else → reject headless idle waiters. Messages are unchanged; only the classification contract moved from wording to a type the owning layer exports.
• No fallback text-matching kept: the packages move together in this workspace, and a fallback would keep the brittleness alive silently.

prompt()'s "already processing" error is intentionally untouched — nothing classifies it.

Tests

No new tests: the three existing precondition assertions in packages/agent now pin the code alongside the message (rejects.toMatchObject), and the one coding-agent test that mocked a plain Error("already processing") to reach the reschedule path is retargeted to throw AgentContinueError("busy", ...) — which also proves plain errors no longer take that path.

Validation

• check/build green
• packages/agent suite 70/70; compaction, compaction-continuation, print-mode, acp-mode suites 91/91

+47/−21 across 8 files.

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Note

Low Risk
Small error-type change with tests updated; classification is more robust, not a behavior change for the intended paths. External callers that still string-match continue() messages would need to switch to the new class/code.

Overview
Callers can classify Agent.continue() precondition failures by stable codes instead of matching error message text.

continue() now throws exported AgentContinueError with busy (active run, retryable) or nothing-to-continue (empty history or trailing assistant turn). Post-compaction continuation in coding-agent branches on those codes: reschedule on busy, ignore nothing-to-continue, reject other errors. prompt() still throws a generic Error.

^{Reviewed by Cursor Bugbot for commit 91856c1. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Replace generic errors with typed AgentContinueError in Agent.continue

• Adds exported AgentContinueError class and AgentContinueErrorCode union ("busy" | "nothing-to-continue") in agent.ts; Agent.continue now throws these instead of generic Error.
• Updates agent-session.ts post-compaction handler to branch on error.code — reschedules on "busy", swallows on "nothing-to-continue", and settles any other error.
• Updates unit, e2e, and compaction tests to assert the new error shape.
• Risk: callers that string-match on the old generic Error.message for Agent.continue precondition failures will no longer match; they must check error instanceof AgentContinueError and error.code instead.

Changes since #1588 opened

• Introduced typed error codes for Agent.continue precondition failures [91856c1]

📊 Macroscope summarized 8c542c0. 1 file reviewed, 1 issue evaluated, 1 issue filtered, 0 comments posted

🗂️ Filtered Issues

packages/ai/.changes/fix-typed-continue-preconditions.md — 0 comments posted, 1 evaluated, 1 filtered

• line 1: This fragment is consumed by scripts/release.mjs into packages/ai's published CHANGELOG.md, but this PR contains no model-catalog/pricing/context-window change in packages/ai; it will therefore publish a false AI release note (and leaves the actual typed-continue change undocumented for that package). Remove this unrelated fragment or replace it with an accurate AI-package change. [ Failed validation ]