refactor(agents): drop the mid-turn compaction min-tokens floor

The `minTokens` guard (default 2000, env ELECTRIC_AGENTS_COMPACT_MIN_TOKENS)
never changed the outcome at any realistic ceiling — 90% of a real context
window is always far above 2000 tokens, so the floor only ever mattered when
testing with an artificially low ceiling. Codex has no equivalent floor (it
triggers on a single token threshold). Remove the knob, its env override, and
the now-unused positiveFromEnv helper.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kevin-dp

.changeset/context-compaction.md

@@ -23,4 +23,4 @@ into a summary):
   "Context compacted" entry in the conversation timeline.
 
 Thresholds are env-tunable (`ELECTRIC_AGENTS_COMPACT_CEILING`,
-`ELECTRIC_AGENTS_COMPACT_BG_CEILING`, `ELECTRIC_AGENTS_COMPACT_MIN_TOKENS`).
+`ELECTRIC_AGENTS_COMPACT_BG_CEILING`).

packages/agents-runtime/src/compaction-midturn.ts

@@ -15,8 +15,6 @@ export interface MidTurnCompactorDeps {
   writeCheckpoint: (status: CompactionStatus, content: string) => void
   /** Compaction fires at/above this fraction of the context window. */
   ceiling: number
-  /** Don't compact unless the context is at least this many tokens. */
-  minTokens: number
   /** Keep this many of the most recent messages verbatim (the live tail). */
   keepTail: number
 }
@@ -77,9 +75,7 @@ export function createMidTurnCompactor(
       : null
 
   return async ({ messages, currentTokens, contextWindow }) => {
-    const overCeiling =
-      currentTokens >= deps.ceiling * contextWindow &&
-      currentTokens > deps.minTokens
+    const overCeiling = currentTokens >= deps.ceiling * contextWindow
 
     // Under the ceiling: keep the compacted view sticky if we already compacted
     // this turn, otherwise leave the context untouched.

packages/agents-runtime/src/context-factory.ts

@@ -37,8 +37,6 @@ import {
 } from './compaction-summarize'
 import { CONTEXT_USAGE_BACKGROUND_START } from './token-accountant'
 
-/** Default minimum context size (tokens) before mid-turn compaction fires. */
-const DEFAULT_COMPACT_MIN_TOKENS = 2000
 /** Recent messages kept verbatim when compacting (the live tool-call tail). */
 const COMPACT_KEEP_TAIL = 6
 import { createContextTools } from './tools/context-tools'
@@ -101,12 +99,6 @@ function ratioFromEnv(raw: string | undefined, fallback: number): number {
   return Number.isFinite(value) && value > 0 && value <= 1 ? value : fallback
 }
 
-/** Parse a positive number from an env string, falling back when invalid. */
-function positiveFromEnv(raw: string | undefined, fallback: number): number {
-  const value = Number(raw)
-  return Number.isFinite(value) && value > 0 ? value : fallback
-}
-
 const MAX_HYDRATED_IMAGE_ATTACHMENTS = 4
 const MAX_HYDRATED_IMAGE_ATTACHMENT_BYTES = 10 * 1024 * 1024
 
@@ -843,19 +835,13 @@ export function createHandlerContext<TState extends StateProxy = StateProxy>(
         // failed checkpoint that drives the UI. Thresholds overridable via env
         // (RFC §12 tunables):
         //   ELECTRIC_AGENTS_COMPACT_CEILING    (0..1, default 0.9)
-        //   ELECTRIC_AGENTS_COMPACT_MIN_TOKENS (default 2000)
         const compactCeiling = ratioFromEnv(
           process.env.ELECTRIC_AGENTS_COMPACT_CEILING,
           CONTEXT_USAGE_HARD_CEILING
         )
-        const compactMinTokens = positiveFromEnv(
-          process.env.ELECTRIC_AGENTS_COMPACT_MIN_TOKENS,
-          DEFAULT_COMPACT_MIN_TOKENS
-        )
         const compactProvider = agentModelProvider(activeAgentConfig)
         const onCompactContext = createMidTurnCompactor({
           ceiling: compactCeiling,
-          minTokens: compactMinTokens,
           keepTail: COMPACT_KEEP_TAIL,
           writeCheckpoint: (status, content) => {
             contextApi.insertContext(COMPACTION_CHECKPOINT_ID, {

packages/agents-runtime/test/compaction-midturn.test.ts

@@ -17,7 +17,6 @@ describe(`createMidTurnCompactor`, () => {
       summarize,
       writeCheckpoint,
       ceiling: 0.9,
-      minTokens: 100,
       keepTail: 4,
     })
     const out = await compact({
@@ -37,7 +36,6 @@ describe(`createMidTurnCompactor`, () => {
       summarize,
       writeCheckpoint,
       ceiling: 0.9,
-      minTokens: 100,
       keepTail: 4,
     })
     const messages = msgs(10)
@@ -62,7 +60,6 @@ describe(`createMidTurnCompactor`, () => {
       summarize,
       writeCheckpoint: vi.fn(),
       ceiling: 0.9,
-      minTokens: 100,
       keepTail: 4,
     })
     const messages = msgs(10)
@@ -88,7 +85,6 @@ describe(`createMidTurnCompactor`, () => {
       summarize,
       writeCheckpoint: vi.fn(),
       ceiling: 0.9,
-      minTokens: 100,
       keepTail: 4,
     })
     await compact({
@@ -114,7 +110,6 @@ describe(`createMidTurnCompactor`, () => {
       summarize,
       writeCheckpoint: vi.fn(),
       ceiling: 0.9,
-      minTokens: 100,
       keepTail: 4,
     })
     // Boundary would land at index 6 (10 − keepTail 4); make that a tool_result
@@ -139,7 +134,6 @@ describe(`createMidTurnCompactor`, () => {
       summarize,
       writeCheckpoint: (s: string) => statuses.push(s),
       ceiling: 0.9,
-      minTokens: 100,
       keepTail: 4,
     })
     const out = await compact({

packages/agents-runtime/test/compaction-trigger.test.ts

@@ -11,11 +11,9 @@ import type { ChangeEvent } from '@durable-streams/state'
 // we drive the trigger with the env override + a high seeded anchor instead.
 const savedEnv = {
   ceiling: process.env.ELECTRIC_AGENTS_COMPACT_CEILING,
-  minTokens: process.env.ELECTRIC_AGENTS_COMPACT_MIN_TOKENS,
 }
 afterEach(() => {
   process.env.ELECTRIC_AGENTS_COMPACT_CEILING = savedEnv.ceiling
-  process.env.ELECTRIC_AGENTS_COMPACT_MIN_TOKENS = savedEnv.minTokens
 })
 
 function completedAssistantMessage(): unknown {
@@ -59,7 +57,6 @@ describe(`mid-turn compaction trigger`, () => {
   it(`compacts mid-turn: summarizer runs, model sees the summary, checkpoint persisted`, async () => {
     // Ceiling tiny so any real model window is crossed by the seeded anchor.
     process.env.ELECTRIC_AGENTS_COMPACT_CEILING = `0.0001`
-    process.env.ELECTRIC_AGENTS_COMPACT_MIN_TOKENS = `10`
 
     // Enough messages that there's real content beyond the kept tail (6).
     const db = buildStreamFixture(