compact: summarize is a direct one-shot llm/stream call, not a loop step

The summarization request no longer dispatches agent/request — that seam
shapes the loop's conversation requests; a hand-built one-shot's
interception surface is llm/stream, like every other direct call. The
model comes from summarizationModel falling back to the agent's own. The
turn/step parameters existed on the compact seam only to feed the
agent/request dispatch and leave compactIfNeeded/compactRegion.

Groundwork for making every conversation request a pure function of the
session log (reconstructability RFC, this branch): the seam split keeps
the loop's request path as the single thing the log must explain.

Ported from worktree-prompt-prefix-stability (PR #162) where it was
review-converged; catalog and producer/consumer graphs regenerated.

packages/compact/compact/src/index.ts

@@ -91,8 +91,6 @@ export abstract class CompactService extends Service {
    *   over-budget. Bounding an individual unit's size is a separate concern.
    *
    * @param agent - agent context owning the session surface and model options.
-   * @param turn - turn number of the pre-step checkpoint.
-   * @param step - step number about to start.
    * @param fullSystemPrompt - assembled system prompt, counted toward the estimate.
    * @param signal - cancellation signal. A backend summarizing via
    *   `ctx.llm.stream()` MUST forward this into the call's `GenerateOptions.signal`
@@ -102,8 +100,6 @@ export abstract class CompactService extends Service {
    */
   abstract compactIfNeeded(
     agent: CompactAgentContext,
-    turn: number,
-    step: number,
     fullSystemPrompt: string,
     signal: AbortSignal,
   ): Promise<CompactionResult | null>
@@ -129,8 +125,6 @@ export abstract class CompactService extends Service {
    * @param start - inclusive seq of the first surface node to compact.
    * @param end - inclusive seq of the last surface node to compact.
    * @param agent - agent context used by router-aware summarizers.
-   * @param turn - lifecycle turn forwarded to request-routing seams.
-   * @param step - lifecycle step forwarded to request-routing seams.
    * @param signal - optional cancellation signal. A backend that summarizes via
    *   `ctx.llm.stream()` MUST forward this into the call's `GenerateOptions.signal`
    *   so an abort/dispose tears down the in-flight summarization rather than
@@ -148,8 +142,6 @@ export abstract class CompactService extends Service {
     start: number,
     end: number,
     agent: CompactAgentContext,
-    turn: number,
-    step: number,
     signal?: AbortSignal,
   ): Promise<CompactionResult>
 }