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:97

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:112

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 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:93

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:123

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:89

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:95

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

turns

readonly turns: readonly Turn[]

Defined in: src/core/agent/window/strategy.ts:66

The same window, segmented into turns.

WindowStrategyInput

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