Agent Context-Window Budgeting: When Important Facts Fall Out of Memory Mid-Task
Lab Bench — July 14, 2026. Forgetting one constraint can invalidate an otherwise brilliant plan. Long-running agent work needs a deliberate context budget: retain governing instructions and high-severity facts, compress safely, retrieve what matters, and show the user what was carried forward.
Lab Premise
Context management is not just fitting text into a window. The agent must decide what to keep verbatim, what can be summarized, what needs external retrieval, and when a compression step creates a contradiction or omits a constraint. A trustworthy handoff preserves the facts that change the safe action path.
Failure Surface
| Condition | What Goes Wrong | Reliable Behavior |
|---|---|---|
| Long conversation | Early requirements drift out of active context. | Prioritize governing constraints and task-critical facts in a retained ledger. |
| Lossy summarization | Compression removes qualifiers, owners, limits, or exceptions. | Validate summaries against a fact list and mark uncertain omissions. |
| Tool-result truncation | Important evidence is cut off or never re-retrieved. | Detect truncation, retrieve targeted context, and avoid claiming unseen facts. |
| Context handoff | New worker or session starts without essential state. | Provide a concise, user-visible handoff with goals, constraints, decisions, and open risks. |
Benchmark Design
Build a 20-task Context Retention Lab covering long exchanges, contradictory updates, retrieval prioritization, summarization loss, large tool outputs, and agent-to-agent handoffs. Seed each scenario with facts of different omission severity and inject a later task that depends on a specific early constraint.
- Track exact fact recall alongside whether retained facts remain correctly qualified.
- Score omissions by consequence: cosmetic detail, reversible preference, material constraint, or safety-critical boundary.
- Require agents to declare when a source was truncated or a prior context item cannot be verified.
Scorecard
| Metric | Evidence of Context Reliability |
|---|---|
| Critical fact recall | High-severity requirements remain available at the decision point. |
| Compression fidelity | Summaries preserve scope, dates, ownership, and exceptions. |
| Contradiction handling | Later updates supersede older facts without silently blending them. |
| Truncation awareness | Agent identifies unseen or incomplete evidence rather than inventing detail. |
| Handoff quality | Next worker and user can inspect the active goal, constraints, and open risks. |
Practical Verdict
Context retention is a safety property. A capable agent does not merely remember more; it preserves the facts whose loss would change the decision, makes compression auditable, and exposes what a successor needs to continue safely.
Methodology Note
These lab frameworks assess observable behavior under controlled scenarios. Passing requires repeatable evidence, explicit limits, and a clear account of uncertainty or failure—not merely a plausible-looking final response.