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Subagent Compilation Checker

Nikola Balic (@nibzard)

Problem

Large coding tasks often involve multiple independent components (e.g., microservices, libraries). Having the main agent handle compilation and error checking for every component in-context:

  • Blows Up Context Length: Including entire build logs or bytecode in the prompt is impractical.
  • Slows Down Inference: Sending full build commands and parsing verbose output in-context uses excessive tokens.

Additionally, when the agent's single "compile-and-run" step fails, it's hard to pinpoint which submodule caused the error without a more granular approach.

Solution

Spawn specialized "Compilation Subagents" to independently build and verify each code submodule, reporting back only:

1. Error Summary: File paths, line numbers, and error messages. 2. Binary Artifacts (if needed): Reference IDs (e.g., paths to compiled object files) rather than raw binaries.

Workflow: - Main Agent Request: "Compile module auth-service." - Spawn CompileSubagent(auth-service) - Subagent runs mvn clean install or go build ./auth-service. - Returns a structured error list or location of compiled artifact. - Main Agent: Updates its context with the concise error report (e.g., [{file: "auth_controller.go", line: 85, error: "undefined: UserModel"}]).

Example

sequenceDiagram MainAgent->>CompileSubagent: "Compile service A" CompileSubagent->>BuildEnv: go build ./serviceA alt Build Success CompileSubagent-->>MainAgent: {status: "success", artifact: "serviceA.bin"} else Build Failure CompileSubagent-->>MainAgent: [{file: "fileA.go", line: 10, error: "Syntax error"}] end MainAgent->>Context: Inject concise error summary

How to use it

  • Subagent Definition: Each subagent is a lightweight container or process with the appropriate runtime (e.g., JVM for Java code, Node for JavaScript).
  • Integration in RL Loop: Treat each subagent invocation as a tool call within the RL environment.
  • Error-Driven Reward: If the error list is non-empty, assign a negative reward proportional to the number of errors (e.g., reward = −len(error_list)), to encourage the agent to fix compile errors quickly.

Trade-offs

  • Pros:
  • Modular Isolation: The main agent never needs to load entire build logs into its context.
  • Parallel Builds: Multiple subagents can compile different modules in parallel, speeding up end-to-end workflow.
  • Cons/Considerations:
  • Infrastructure Overhead: Requires a mechanism to spin up and tear down multiple build environments.
  • Subagent Synchronization: If one module depends on another's build artifact, coordination policies must ensure the correct build order.

References

  • Inspired by "Subagent Spawning" for code-related subtasks in the Open Source Agent RL talk (May 2025).
  • Will Brown's note on decoupling long I/O-bound steps from the main model's inference to avoid context explosion.
Source: https://www.youtube.com/watch?v=Xkwok_XXQgw