What the provider REPORTED for the last completed call. Counted, never guessed. undefined before the first call of the run — a strategy that acted on that would be guessing, which is the one thing this family refuses to do.

{ input: 0, output: 0 } is a provider that reported NOTHING, not a call that cost nothing. A token-triggered strategy should throw CompactionUnmeasurableError there rather than invent a size.

now

readonly now: () => number

Defined in: src/core/agent/window/strategy.ts:100

Wall clock, injectable so a caller can pin survivalMs.

Returns

number

planRemoval

readonly planRemoval: (keepRecentTurns, isExistingSummary?) => RemovalPlan

Defined in: src/core/agent/window/strategy.ts:115

THE shared refusal engine, bound to this iteration.

Answers: which contiguous span of turns may leave, and every turn that refused, named. Never removes the system envelope, the CURRENT REQUEST, the last keepRecentTurns turns, an unanswered tool call, the paused tool, or a pending check-in.

Parameters

keepRecentTurns

number

how many trailing turns are off-limits

isExistingSummary?

(turn) => boolean

optional predicate marking a turn that is a summary a previous fold wrote; when the whole span is one of those, the plan refuses with only-existing-summary. Pass it only if your strategy spends an LLM call — a drop has nothing to protect against.

Returns

RemovalPlan

providerName

readonly providerName: string

Defined in: src/core/agent/window/strategy.ts:96

provider.name of the MAIN provider, for a refusal that names it.

removalFacts

readonly removalFacts: (indices, atMs) => RemovalFacts

Defined in: src/core/agent/window/strategy.ts:126

Turn removed message indices into the facts the ledger needs: which stages wrote them, and how long each lived in the window.

Parameters

indices

readonly number[]

indices in the PRE-change window that are leaving

atMs

number

the moment they leave (usually input.now())

Returns

RemovalFacts

runId

readonly runId: string

Defined in: src/core/agent/window/strategy.ts:92

The run this decision belongs to.

A strategy that retains what it removed has to name the run whose commit log held it — that is the honest answer to "where else could I have found this?", and the answer is "nowhere, once that process ended", which is the whole reason retention exists. 'unknown' when the runtime could not name the run, never a fabricated id.

signal

readonly signal: AbortSignal | undefined

Defined in: src/core/agent/window/strategy.ts:98

The run's cancellation signal, when there is one.

turns

readonly turns: readonly Turn[]

Defined in: src/core/agent/window/strategy.ts:69

The same window, segmented into turns.

WindowStrategyInput

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