Context Curation

An agent is only as good as what's in its context window. Too little and it guesses; too much and the signal drowns in noise. Models also lose focus in the middle of long contexts — burying the important bit under thousands of tokens of "related" material doesn't make work safer, it makes it worse.

Curate deliberately: load what the current step needs, ground it in authoritative sources, and prune what no longer matters. Context curation is not a one-time setup — it's ongoing hygiene for every step of a task.

Pairs with [[source-first]] for what to load, [[work-planning]] for step boundaries, [[incremental-delivery]] for slice-sized working sets, and [[decision-docs]] for durable "why" that shouldn't live in chat.

When to Use

• A task touches a large codebase and you must choose what to show the agent
• Responses drift, repeat, hedge, or invent files/APIs that don't exist
• You're writing or reorganizing project rules, CLAUDE.md, AGENTS.md, or Cursor rules
• A long session is degrading — slower, vaguer, or contradicting earlier decisions
• Designing LLM prompts, system instructions, RAG retrieval, or agent tool payloads ([[llm-feature-engineering]])
• Handing work to another person or a fresh session and need a clean starting point
• Multiple skills or large reference docs are tempting you to "load everything just in case"

Skip as the primary skill for a trivial one-file edit with no drift — but still apply the working-set habit. Never skip when setting up standing instructions; bad project memory poisons every future task.

Process

Work in order. Later steps assume you've classified what kind of context you're managing.

1. Classify what you're holding

Context isn't one blob. Separate it mentally (and in project files) into layers:

Rule: standing rules are tiny and stable; working set is large only for the moment you need it, then collapses to a conclusion.

2. Define the working set for this step

Before reading or pasting anything, write (in chat or a scratch note) a one-line step goal and the minimum material required to achieve it. Pair with [[work-planning]] when the task has multiple steps.

Include only:

• The function, type, or module you're changing — not every file in the directory
• Contracts the change must honor: API schema, interface, public types, event shape
• One example of correct usage or test — not every test in the suite
• The error or symptom — stack trace, log line, failing test name — for debugging
• Explicit out-of-scope — "do not touch billing," "ignore legacy v1 endpoints"

Resist:

• "Everything in src/features/"
• Whole files when one exported function matters
• Duplicating code already in the repo as a pasted paraphrase
• Loading five skills because the task is "big"

Step goal: Fix null handling in OrderSummary when cart is empty.

Working set:
  - components/OrderSummary.tsx (render + props)
  - types/cart.ts (CartSummary shape)
  - OrderSummary.test.tsx (empty-cart case)

Out of scope: checkout flow, payment APIs, other cart components

3. Load precisely — search wide, read narrow

Retrieval strategy:

1. Search (grep, semantic search, symbol lookup) to find candidates.
2. Read only the matched region — function, type block, config key — not the whole file.
3. Trace one call path for behavior questions; don't load every importer ([[source-first]]).
4. Prefer pointers — file path + line range — over pasting full source into chat.
5. One skill at a time — load the skill for the current phase ([[skill-router]]), not the whole catalog.

When a file is huge:

• Read the export/signature first, then the implementation you touch.
• Skip generated code, lockfiles, and vendor bundles unless the bug is there.
• For configs, load the key you need — not every environment block.

4. Ground in authoritative sources

Paraphrase is a lossy compression that invents details. Load the real artifact:

• Code and types over your memory of the API
• Installed version over docs for a different release
• Schema/OpenAPI over a Slack description of the endpoint
• Failing test output over a guess at what failed

If you must summarize for another session, summarize conclusions ("CartSummary.items is optional when empty") — not a hand-wavy recreation of the code. See [[source-first]].

5. Front-load rules, lazy-load detail

Standing instructions should be:

• Short — if rules exceed a few screens, agents skim and miss the critical line
• Specific — "validate at API boundary" beats "handle errors properly"
• Non-contradictory — pick one convention; delete the stale rule
• Stable — task-specific detail belongs in the ticket, not CLAUDE.md

Task detail loads on demand when that task is active. Don't put "how to run the e2e suite for feature X" in global rules if only feature X work needs it.

When writing rules, link to deeper docs instead of duplicating them:

<!-- Good -->
API errors: use `ApiError` shape in `lib/errors.ts`. See ADR-012 for why we don't throw raw strings.

<!-- Bad -->
API errors: sometimes we use ApiError, but legacy routes return { error: string } except on Tuesdays...

6. Prune and summarize as you go

Context fills with transcripts. Treat finished work as outcomes, not play-by-play.

After each sub-task or slice ([[incremental-delivery]]):

• Collapse exploration: "Tried A and B; B works because cache key includes tenant."
• Drop superseded code snippets from chat — the repo has the truth.
• Remove failed hypotheses unless they prevent repeat mistakes.
• Keep decisions and constraints: "We must not add a DB round-trip here — perf budget."

Signs you need to prune now:

• The same file was pasted three times
• A 20-message debugging thread with no stated conclusion
• Instructions repeated because "the agent forgot"

7. Re-anchor on long tasks

On multi-step or multi-session work, periodically restate a state block (every few steps or when quality dips):

Goal: Add guest checkout (spec §3.2).
Done: cart merge, guest session cookie, OrderSummary empty state.
Current: payment redirect — investigating 422 on POST /api/orders.
Constraints: no new DB tables; must work with existing Stripe webhook.
Next: trace validateOrderPayload → fix schema mismatch.
Not doing: account creation upsell (out of scope).

Re-anchor beats silent drift. If re-anchoring doesn't help — context is polluted beyond recovery — start a fresh session with a tight brief and the state block, not the full old transcript.

8. Maintain durable project memory

When you discover something every future agent should know:

• Convention → short rule in CLAUDE.md or project rules
• Significant choice → ADR or decision doc ([[decision-docs]])
• Repeatable process → skill in this repo ([[skill-creator]])

Audit standing memory when:

• Agents keep making the same wrong assumption
• Two rules contradict each other
• A rule describes code that no longer exists
• New hires (or agents) ask the same "why" question

Delete or supersede stale rules. Wrong memory is worse than none.

9. Scenario playbooks

Large feature across many files

• Plan steps first ([[work-planning]]); one working set per step.
• Each slice: load only what that slice touches; summarize before the next slice.
• Don't load the whole spec every turn — load the current section.

Debugging

• Working set: error message, stack, inputs, one reproduction path.
• Trace until the mismatch is found; don't load unrelated modules.
• State the root cause in one sentence before fixing.

Code review

• Diff + files that define contracts the diff relies on.
• Don't load the entire codebase to "understand context."
• If review needs architecture why, load the ADR — not five adjacent services.

Session handoff

• Write a state block (goal, done, current, constraints, next).
• Link paths, not pasted code.
• Fresh session starts from the block + narrow working set.

Subagents and parallel exploration

• Isolate heavy search in a subagent; parent keeps summary + pointers.
• Parent context should not absorb every file the subagent read.

LLM prompts and tools

• Same rules: minimal grounded context per call.
• Retrieve facts; don't stuff the whole knowledge base.
• Validate tool payloads — don't pass unbounded user text ([[llm-feature-engineering]], [[hardening]]).

10. Resolve contradictions before loading

Conflicting instructions produce hedging, wasted tokens, and wrong compromises.

Before adding or loading rules:

• Search for an existing rule on the same topic.
• Pick one convention; remove or supersede the other.
• If both are valid in different layers, scope them: "In legacy/ use X; in api/v2/ use Y."

Never load two skills whose processes conflict for the same step without choosing which governs.

Common Rationalizations

• "More context is safer." — Past a point, extra context lowers accuracy and hides the relevant bits.
• "I'll paste the whole file." — Show the function that matters; the rest is noise the model must wade through.
• "It remembers what we discussed." — Detail decays as the window fills; re-anchor or restart with a state block.
• "One big rules file covers it." — Rules that contradict or over-specify confuse more than they help.
• "I'll load all the skills so nothing is missed." — Agents follow none of them fully; load one for the current phase.
• "Paraphrasing the API is faster than reading it." — Paraphrase invents parameters; read the signature.
• "The transcript is fine — I need the history." — History without summary is a pile of noise; collapse to outcomes.
• "We'll clean up CLAUDE.md later." — Every session pays the cost of stale or conflicting rules until you do.

Red Flags

• Dumping entire directories or monorepo packages into context "for completeness"
• The agent references files, functions, or APIs that don't exist
• Quality dropping as the session grows — vaguer answers, repeated mistakes
• Standing instructions that contradict each other or describe deleted code
• The same code or explanation pasted repeatedly instead of summarized once
• Five skills loaded for one task; none followed completely
• Debugging with no stated reproduction path or error text in context
• CLAUDE.md or rules files longer than a few screens with no clear hierarchy
• Handoff is "read the whole chat" instead of a state block and pointers
• Prompt or tool design that passes unbounded context every call

Verification

• [ ] Context layers identified — standing rules vs task brief vs step working set
• [ ] Step goal and minimum working set written before bulk loading
• [ ] Out-of-scope explicitly stated for the current step
• [ ] Search wide, read narrow — functions/regions, not whole directories
• [ ] Authoritative sources loaded ([[source-first]]); no invented APIs from paraphrase
• [ ] Only the skill(s) for the current phase loaded ([[skill-router]])
• [ ] Finished sub-tasks collapsed to conclusions; duplicate snippets removed
• [ ] Long task re-anchored with goal, done, current, constraints, next — or fresh session with state block
• [ ] Standing rules are short, specific, non-contradictory, and stale rules removed or superseded
• [ ] Handoffs use state block + paths, not full transcript replay