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CCAR-F - Claude Code Configuration & Workflows - Section 3.4

Determine when to use plan mode versus direct execution.

Plan mode suits large-scale changes, several valid approaches, architectural decisions and multi-file modifications, because it allows safe exploration and design before any change and prevents costly rework. Direct execution suits a simple well-scoped change such as one validation check in one function. Candidates should also use an exploration subagent to isolate verbose discovery output, and should combine plan mode for investigation with direct execution for the implementation itself.

plan modedirect executionarchitectural implicationsExplore subagentcontext window exhaustion during discovery

Practice question for this objective

Free sampleClaude Code Configuration & Workflowsmedium

Northwind's checkout service holds about 400 source files. A developer asks Claude Code, in direct execution, to find every caller of a deprecated pricing helper and update them. The session reads 38 files inline, the context window fills during discovery, and the run is restarted before a single edit lands. A colleague reruns the same task by first dispatching the Explore subagent to locate the callers, then editing in the main session, and the run completes. Which mechanism explains why the second run has room left for the edits?

  • AThe Explore subagent works in its own context window and returns the paths and line references it concluded with, so the bodies of the files it read stay out of the main session's window. Correct
  • BThe Explore subagent reads source files in a compressed representation that costs fewer tokens per file, so the same 38 files occupy a small fraction of the main session's context window.
  • CThe Explore subagent continues inside the main session's conversation, so its reads are deduplicated against the files that session already opened and only the new callers are added to the window.
  • DThe Explore subagent forces the main session to compact before it begins, so the earlier turns are summarised and the reclaimed window is what the subsequent edits are then written into.
Delegating discovery to a subagent keeps raw file contents in the subagent's context, returning only a conclusion to the main session. Context exhaustion during discovery is a placement problem. Read inline, each of the 38 files lands permanently in the main session's window and competes with the edits that follow. Dispatched to a subagent, the same reads land in a separate window that is discarded when the subagent finishes, and the coordinator receives a short report instead. The token cost of looking is paid somewhere that does not have to hold the work.

Why A is correct: Correct. A dispatched subagent holds a separate context, and only its final report crosses back, so discovery that would have cost tens of thousands of tokens inline arrives as a short answer.

Why B is wrong: Tempting because the subagent clearly handles more material than the main session could, but there is no cheaper encoding of file contents; the saving comes from where the contents are held, not from how they are represented.

Why C is wrong: Tempting because the subagent is dispatched from the session and reports back to it, but a subagent does not share the coordinator's conversation; treating it as continuing that conversation is the classic inheritance error.

Why D is wrong: Tempting because compaction is a real way to reclaim a window, but dispatching a subagent does not trigger it; the second run simply never accumulated the file contents in the first place.

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