docs: rebalance prose cleanup and add trimming skill

packages/core/session/tests/derived-cache.spec.ts

@@ -1,4 +1,8 @@
-/** Derived-message cache behavior against a from-scratch replay oracle. */
+/**
+ * Derived-message cache contract against a scratch oracle: project new nodes
+ * once, rebuild on surface generation changes, return fresh arrays over shared
+ * frozen messages, and remain value-equal to replay at every step.
+ */
 
 import { describe, expect, it } from 'vitest'
 import { Session, SessionId } from '@deepseek-ai/dsh-session'

packages/core/session/tests/properties.spec.ts

@@ -13,8 +13,8 @@ import { CallId } from '@deepseek-ai/dsh-llm'
 import { Session, SessionId } from '@deepseek-ai/dsh-session'
 import type { SessionEventMap, SessionEventType, SurfaceIntent } from '@deepseek-ai/dsh-session'
 
-// An appendable event: its type/data plus, for surface-eligible types, the explicit surface
-// intent the generator declares (mirroring how a real caller passes it).
+// Each arbitrary supplies its own surface intent; `build` must not synthesize
+// one or the property would fail to exercise malformed fixture choices.
 type Appendable = {
   [T in SessionEventType]: { type: T; data: SessionEventMap[T]; intent?: SurfaceIntent }
 }[SessionEventType]

packages/core/session/tests/repair.spec.ts

@@ -155,9 +155,8 @@ describe('interruptedTurnClosers', () => {
   })
 
   it('handles tool/call without a matching assistant/message entry gracefully', () => {
-    // A tool/call event exists in the log but no assistant/message registered the callId in
-    // pendingCalls (e.g., a plugin appended it directly, or the assistant/message from a prior
-    // step didn't have this call).
+    // A raw tool/call with no assistant-registered pending call has nothing to
+    // answer; repair still closes the step and turn without synthesizing a result.
     const events: SessionEvent[] = [
       userTurnStart(1, 0),
       { type: 'step/start', seq: 1, time: 1, data: { turn: 1, step: 1 } },

packages/core/session/tests/session.spec.ts

@@ -129,8 +129,8 @@ describe('Session', () => {
   it('rejects a surface-eligible append with no surfaceOp marker (runtime guard for the union-widening loophole)', () => {
     const session = new Session(SessionId('s5b'))
     session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
-    // The typed overload makes surfaceOp mandatory only when the type argument is a SPECIFIC
-    // SurfaceEventType literal.
+    // A widened SessionEventType bypasses the overload's conditional requirement,
+    // so the runtime guard must still reject the missing surface marker.
     const widenedType = 'user/message' as SessionEventType
     expect(() => session.append(widenedType, { content: [{ type: 'text', text: 'hi' }], source: { kind: 'user' } }))
       .toThrow(/surface-eligible and requires a surfaceOp marker/)
@@ -657,8 +657,8 @@ describe('SessionStore', () => {
   })
 
   it('enter() rejects a stale prepared session whose id is already live (no overwrite)', async () => {
-    // prepare()/enter() are public cross-package primitives that a caller may separate with
-    // arbitrary work.
+    // A stale prepared object must not replace the live same-id entry; its later
+    // detach would otherwise remove the wrong session.
     const ctx = new Context()
     await ctx.plugin(SessionStore)
     const stale = ctx.sessions.prepare(SessionId('racy'))

packages/core/session/tests/surface.spec.ts

@@ -70,14 +70,11 @@ describe('SurfaceManager', () => {
 
   it('rebuild with replace operation splices out shadowed nodes', () => {
     const s = surfaceSession()
-    // seq: 0=turn/start, 1=user, 2=assistant, 3=turn/end
-    // Surface nodes: seq 1 (user), seq 2 (assistant).
-    // Replace both with a compaction marker. Both 1 and 2 are valid surface seqs.
+    // Replace surface seqs 1 (user) and 2 (assistant) with the summary.
     s.append('assistant/message',
       { turn: 2, step: 1, content: [{ type: 'text', text: 'summary' }] },
       { surfaceOp: { op: 'replace', start: 1, end: 2 }, sourceEventSeqs: [1, 2] },
     )
-    // Now the surface should have just the compaction node.
     expect(s.surface.nodes.length).toBe(1)
     expect(s.surface.nodes[0]!.seq).toBe(4) // seq of the compaction marker
     expect(s.surface.nodes[0]!.prev).toBeNull()

packages/core/session/tests/tool-pairing.spec.ts

@@ -4,7 +4,9 @@ import { Session, SessionId, isToolPairingBalanced } from '../src/index.ts'
 import type { SessionEvent, SurfaceNode } from '../src/index.ts'
 
 /**
- * Unit coverage for the tool-pairing balance check.
+ * Unit coverage for compaction-cut safety: a cut is balanced only when it
+ * separates no assistant tool call from its result. Non-step nodes are neutral,
+ * and replace operations prove surface order—not raw log order—is authoritative.
  */
 
 const SURFACE = { surfaceOp: 'append' as const }
@@ -165,8 +167,8 @@ describe('isToolPairingBalanced — multiple tool calls in one assistant message
 })
 
 describe('isToolPairingBalanced — a mid-step injection context/message', () => {
-  // A background task-done inject() lands a context/message inside an open step, between the
-  // assistant (with a tool-call) and its tool/result.
+  // The injected context is pairing-neutral, but both adjacent cuts remain
+  // unbalanced because the tool call is still open across them.
   function midStepInjection(): Session {
     const s = new Session(SessionId('mid-inject'))
     s.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
@@ -217,7 +219,8 @@ describe('isToolPairingBalanced on an injection turn (no step)', () => {
 })
 
 describe('isToolPairingBalanced — CBR-001: a head checkpoint left by a replace op', () => {
-  // The case the log-position scan got wrong.
+  // A replacement checkpoint has a high log seq but sits at the surface head;
+  // its cuts are balanced regardless of later raw-log neighbors.
   function checkpointHeadedSession(): Session {
     const s = new Session(SessionId('checkpoint'))
     // A closed turn with a tool step → surface [u1, asst(call), result].