feat(compact): prune tool results before summarization (round 1)

packages/support/invariants/README.md

@@ -31,7 +31,7 @@ Session log (per session):
 - **turns pair and nest** — `turn/start` opens a turn, `turn/end` closes the matching one; no overlapping turns.
 - **steps nest in turns** — `step/start` opens a step in the open turn; `step/end` closes the matching step.
 - **chunks belong to an open step** — `step/start` precedes its `assistant/chunk`s.
-- **a `tool/result` needs a prior `tool/call`** — but NOT the converse: a `tool/call` may have no result (a thrown tool-execution pipeline step ends the turn with no `tool/result`, which is legal).
+- **an appended `tool/result` needs a prior `tool/call`** — fresh `surfaceOp: 'append'` results name the open step and consume its pending call, while a provenance-backed single-node `replace` is a turn-enclosed surface rewrite of an already-executed result. A `tool/call` may still have no result when the execution pipeline throws.
 - **provenance sources are valid and unambiguous** — `sourceEventSeqs` contains unique earlier known seqs; only `assistant/message` may carry an explicit empty list, which denotes a known empty provider stream rather than absent legacy provenance.
 
 Agent status (per agent):

packages/support/invariants/src/index.ts

@@ -232,6 +232,17 @@ function validateEvent(trace: SessionTrace, event: SessionEvent): SessionTraceTr
       break
     }
     case 'tool/result': {
+      // A replacement rewrites an already-executed result whose recorded
+      // turn/step can be closed. Surface provenance above validates the rewrite;
+      // only fresh appends consume an open step's pending call.
+      if (se.surfaceOp !== undefined && se.surfaceOp !== 'append') {
+        if (trace.openTurn === null) {
+          throw new InvariantError(
+            'tool/result surface replacement appended outside any open turn',
+          )
+        }
+        break
+      }
       requireOpenStep(trace, 'tool/result', event.data.turn, event.data.step)
       // A result needs a prior matching call in the same step. (The converse
       // does NOT hold: a call may have no result — a throwing tool-execution

packages/support/invariants/tests/invariants.spec.ts

@@ -189,6 +189,19 @@ describe('session-log invariants', () => {
       .toThrow(/no prior tool\/call/)
   })
 
+  it('keeps fresh tool-result appends open-step and pending-call checked', async () => {
+    const { ctx } = await setup()
+    const session = ctx.sessions.create()
+    session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+    expect(() => session.append('tool/result', {
+      turn: 1,
+      step: 1,
+      callId: CallId('closed'),
+      content: [],
+      isError: false,
+    }, { surfaceOp: 'append' })).toThrow(/open is turn 1\/step null/)
+  })
+
   it('allows a synthetic interrupted tool/result from crash repair without a prior tool/call event', async () => {
     const { ctx } = await setup()
     const session = ctx.sessions.create()
@@ -487,6 +500,38 @@ describe('surface invariants', () => {
     // no throw — well-formed replace op
   })
 
+  it('treats a provenance-backed tool-result replacement as a turn-enclosed rewrite', async () => {
+    const { ctx } = await setup()
+    const session = ctx.sessions.create()
+    session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+    session.append('step/start', { turn: 1, step: 1 })
+    session.append('tool/call', {
+      turn: 1,
+      step: 1,
+      callId: CallId('rewrite'),
+      name: 'echo',
+      arguments: '{}',
+    })
+    const original = session.append('tool/result', {
+      turn: 1,
+      step: 1,
+      callId: CallId('rewrite'),
+      content: [{ type: 'text', text: 'original' }],
+      isError: false,
+    }, { surfaceOp: 'append' })
+    session.append('step/end', { turn: 1, step: 1 })
+    session.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
+    session.append('turn/start', { turn: 2, trigger: { kind: 'message', source: { kind: 'user' } } })
+
+    expect(() => session.append('tool/result', {
+      ...original.data,
+      content: [{ type: 'text', text: 'pruned' }],
+    }, {
+      surfaceOp: { op: 'replace', start: original.seq, end: original.seq },
+      sourceEventSeqs: [original.seq],
+    })).not.toThrow()
+  })
+
   it('accepts known-empty assistant provenance and rejects empty provenance elsewhere', async () => {
     const { ctx } = await setup()
     const session = ctx.sessions.create()