/fable-context-thrift

name: fable-context-thrift
description: Use at the start of any multi-step task and during exploration — before reading files, searching, or re-checking completed work, especially when tempted to read whole files, re-verify known facts, or run independent lookups one at a time.

Context Thrift

Overview

Context is the budget everything else is paid from. Spend it on what changes your next action; nothing else.

Rules

1. **Independent calls go in one parallel block.** Multiple greps, reads, status checks — batch them. Sequencing independent reads adds latency, not care. 2. **Read targeted.** The symbol or section, not the file. Widen only when a specific question demands it. 3. **Delegate sweeps, keep lookups.** Broad questions ("where is X handled", find-all-usages in unfamiliar territory) go to a search subagent if available — keep the conclusion, not the file dumps. Known single lookups stay direct. "The subagent is for when I *don't* know where things live." 4. **The tool is the confirmation.** Never re-read a file to check an edit landed; the edit tool fails loudly. Verify outcomes with one cheap end-state check (a grep for the old token), not per-file re-reads. 5. **Established facts stay established.** What the conversation already verified, don't re-derive. What the user already decided, don't reopen. 6. **Don't narrate options you won't pursue.** Deliberation is for choices you might actually make. 7. **Enough-to-act test.** If more exploration would not change your next action, exploration is over. Act.

Rationalizations

| Thought | Reality | |---|---| | "I'll read the whole file for context" | Read what the change touches. The question you're answering defines the lines you need. | | "Let me just double-check my edit landed" | The tool reported success; silence is success. One end-state grep beats N re-reads. | | "One more search to be safe" | If the result wouldn't change your action, it isn't safety — it's stalling with receipts. | | "I'll re-verify the repo layout first" | It's in your context and was correct an hour ago. Directory trees don't rot mid-session. | | "Careful means one call at a time" | Careful means right calls. Independent lookups in sequence is the same work, slower. | | "I'll dispatch a subagent to be thorough" | On a 40-file repo, grep returns line-level truth faster than a subagent returns prose. Match the tool to the territory. |

Provenance: mostly predicted — Opus 4.8 baseline-passed this scenario (quotes above are its own passing-run words). fable-skills test logs, 2026-06-10.

Red Flags — stop spending

• A Read call for a file you edited this turn
• The same fact verified twice in one session
• Sequential tool calls with no data dependency between them
• An exploration step you can't name the decision for
• Whole-file reads where a grep already gave you the line numbers