diff --git a/apps/server/src/schema.sql b/apps/server/src/schema.sql
index 78e9ac5..9be69f6 100644
--- a/apps/server/src/schema.sql
+++ b/apps/server/src/schema.sql
@@ -56,6 +56,24 @@ CREATE TABLE IF NOT EXISTS message_parts (
 );
 CREATE INDEX IF NOT EXISTS message_parts_msg_seq_idx ON message_parts (message_id, sequence);
 
+-- v1.13.4: prune support. hidden_at marks parts that have been pruned out
+-- of the model payload by the two-tier compaction prune (services/inference/
+-- prune.ts). Rows stay in the DB so frontend can still display them with a
+-- "hidden" indicator (out of scope this dispatch). messages_with_parts
+-- view filters these out — see below. Partial index speeds the common
+-- "visible parts only" filter.
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1 FROM information_schema.columns
+    WHERE table_name = 'message_parts' AND column_name = 'hidden_at'
+  ) THEN
+    ALTER TABLE message_parts ADD COLUMN hidden_at timestamptz NULL;
+  END IF;
+END $$;
+CREATE INDEX IF NOT EXISTS message_parts_hidden_idx
+  ON message_parts (message_id) WHERE hidden_at IS NULL;
+
 -- v1.13.1-B: read-path view. Read sites SELECT FROM messages_with_parts
 -- instead of messages so tool_calls / tool_results / reasoning_parts come
 -- from the granular message_parts table. The COALESCE means pre-v1.13.0
@@ -73,23 +91,32 @@ SELECT
   m.last_seq, m.tokens_used, m.ctx_used, m.ctx_max,
   m.started_at, m.finished_at, m.created_at, m.metadata,
   m.summary, m.tail_start_id, m.compacted_at,
-  COALESCE(
-    (SELECT jsonb_agg(p.payload ORDER BY p.sequence)
-       FROM message_parts p
-      WHERE p.message_id = m.id AND p.kind = 'tool_call'),
-    m.tool_calls
-  ) AS tool_calls,
-  COALESCE(
-    (SELECT p.payload
-       FROM message_parts p
-      WHERE p.message_id = m.id AND p.kind = 'tool_result'
-      ORDER BY p.sequence
-      LIMIT 1),
-    m.tool_results
-  ) AS tool_results,
+  -- v1.13.4: prune semantics need to distinguish "no parts row exists"
+  -- (pre-v1.13.0 fallback to legacy column) from "all parts hidden"
+  -- (prune intended — return null/empty so the row drops from the model
+  -- payload). A naive COALESCE would fall back to the legacy column when
+  -- every part is hidden, undoing the prune. CASE on EXISTS(any kind)
+  -- splits the two cases.
+  CASE
+    WHEN EXISTS (SELECT 1 FROM message_parts pp
+                  WHERE pp.message_id = m.id AND pp.kind = 'tool_call')
+    THEN (SELECT jsonb_agg(p.payload ORDER BY p.sequence)
+            FROM message_parts p
+           WHERE p.message_id = m.id AND p.kind = 'tool_call' AND p.hidden_at IS NULL)
+    ELSE m.tool_calls
+  END AS tool_calls,
+  CASE
+    WHEN EXISTS (SELECT 1 FROM message_parts pp
+                  WHERE pp.message_id = m.id AND pp.kind = 'tool_result')
+    THEN (SELECT p.payload
+            FROM message_parts p
+           WHERE p.message_id = m.id AND p.kind = 'tool_result' AND p.hidden_at IS NULL
+           ORDER BY p.sequence LIMIT 1)
+    ELSE m.tool_results
+  END AS tool_results,
   (SELECT jsonb_agg(p.payload ORDER BY p.sequence)
      FROM message_parts p
-    WHERE p.message_id = m.id AND p.kind = 'reasoning') AS reasoning_parts
+    WHERE p.message_id = m.id AND p.kind = 'reasoning' AND p.hidden_at IS NULL) AS reasoning_parts
 FROM messages m;
 
 ALTER TABLE messages ADD COLUMN IF NOT EXISTS tokens_used INTEGER;
diff --git a/apps/server/src/services/__tests__/prune.test.ts b/apps/server/src/services/__tests__/prune.test.ts
new file mode 100644
index 0000000..c7ec365
--- /dev/null
+++ b/apps/server/src/services/__tests__/prune.test.ts
@@ -0,0 +1,96 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import {
+  selectPruneTargets,
+  PROTECTED_TOKENS,
+  PRUNE_TRIGGER_TOKENS,
+  type PartForPrune,
+} from '../inference/prune.js';
+
+// Test fixture: build a tool_result part whose payload size yields a known
+// token estimate (chars/4). The decision logic only cares about
+// JSON.stringify(payload).length, so a string payload of `4n` chars
+// produces exactly `n` tokens.
+let seq = 0;
+function part(tokens: number, createdAt: Date): PartForPrune {
+  seq += 1;
+  // JSON.stringify("xxx...") wraps in quotes (adds 2 chars), so subtract 2
+  // before multiplying. Math.ceil((len+2)/4) needs len ≈ 4*tokens - 2 so the
+  // total stringified length is 4*tokens. Approximate by padding 4 chars per
+  // token; the off-by-one from quotes is small and tests check totals, not
+  // exact per-part counts.
+  const text = 'x'.repeat(tokens * 4 - 2);
+  return { id: `p${seq}`, payload: text, created_at: createdAt };
+}
+
+const T_NOW = new Date('2026-05-22T12:00:00Z');
+function ago(secondsBack: number): Date {
+  return new Date(T_NOW.getTime() - secondsBack * 1000);
+}
+
+describe('selectPruneTargets', () => {
+  beforeEach(() => {
+    seq = 0;
+  });
+
+  it('returns nothing when there are no parts', () => {
+    expect(selectPruneTargets([], null)).toEqual({ ids: [], freedTokens: 0 });
+  });
+
+  it('returns nothing when total tokens are under the protection window', () => {
+    const parts: PartForPrune[] = [
+      part(10_000, ago(10)),
+      part(10_000, ago(20)),
+    ]; // 20k total, all protected
+    expect(selectPruneTargets(parts, null)).toEqual({ ids: [], freedTokens: 0 });
+  });
+
+  it('returns nothing when candidate total is below the prune trigger', () => {
+    // Protection fills with ~40k newest, candidates only ~5k. Below 20k trigger.
+    const parts: PartForPrune[] = [
+      part(20_000, ago(10)),
+      part(20_000, ago(20)),
+      // Past protection; total ~5k won't trigger.
+      part(5_000, ago(30)),
+    ];
+    const result = selectPruneTargets(parts, null);
+    expect(result.ids).toEqual([]);
+    expect(result.freedTokens).toBe(0);
+  });
+
+  it('hides candidates past protection when their total clears the trigger', () => {
+    // Newest 40k protected; older 30k cleanly above the 20k trigger.
+    const parts: PartForPrune[] = [
+      part(20_000, ago(10)),
+      part(20_000, ago(20)),
+      // Past protection, total ~30k freed.
+      part(15_000, ago(30)),
+      part(15_000, ago(40)),
+    ];
+    const result = selectPruneTargets(parts, null);
+    expect(result.ids).toEqual(['p3', 'p4']);
+    expect(result.freedTokens).toBeGreaterThanOrEqual(PRUNE_TRIGGER_TOKENS);
+  });
+
+  it('stops at the compaction summary boundary', () => {
+    // Newest 30k protected (just under PROTECTED_TOKENS=40k); then 30k of
+    // older parts. Boundary sits at ago(35), so the ago(40) part is
+    // beyond it and gets skipped.
+    const parts: PartForPrune[] = [
+      part(15_000, ago(10)),
+      part(15_000, ago(20)),
+      part(15_000, ago(30)), // crosses protection threshold; candidate
+      part(15_000, ago(40)), // beyond summary boundary; skipped
+    ];
+    const tailStart = ago(35);
+    const result = selectPruneTargets(parts, tailStart);
+    // ago(30) is the only candidate inside the window; 15k is below the
+    // 20k trigger so we expect no hides.
+    expect(result.ids).toEqual([]);
+  });
+
+  it('does not prune when only protected parts exist (no candidates)', () => {
+    // Exactly PROTECTED_TOKENS of newest parts; no older candidates.
+    const parts: PartForPrune[] = [part(PROTECTED_TOKENS, ago(10))];
+    expect(selectPruneTargets(parts, null)).toEqual({ ids: [], freedTokens: 0 });
+  });
+});
diff --git a/apps/server/src/services/inference/payload.ts b/apps/server/src/services/inference/payload.ts
index 84c579b..f5c11f9 100644
--- a/apps/server/src/services/inference/payload.ts
+++ b/apps/server/src/services/inference/payload.ts
@@ -8,6 +8,7 @@ import type {
 import * as compaction from '../compaction.js';
 import { buildSystemPrompt } from '../system-prompt.js';
 import { isAnySentinel } from './sentinels.js';
+import { PRUNE_TRIGGER_TOKENS, prune } from './prune.js';
 import type { InferenceContext } from './turn.js';
 
 export interface OpenAiMessage {
@@ -166,6 +167,26 @@ export async function maybeFlagForCompaction(
     contextLimit,
   );
   if (!overflow) return;
+
+  // v1.13.4: try the cheap prune first. If it freed at least the buffer
+  // worth of tokens (PRUNE_TRIGGER_TOKENS, identical to COMPACTION_BUFFER),
+  // we're below the threshold again — skip flagging summarize for the next
+  // turn. The next turn's overflow check will re-evaluate from scratch.
+  // Prune failures (DB errors etc.) propagate so the surrounding inference
+  // path sees them; the catch in finalizeCompletion / executeToolPhase
+  // doesn't shield this — by design, we want to know if prune is broken.
+  const pruned = await prune({ sql: ctx.sql, chatId });
+  if (pruned.hidden > 0) {
+    ctx.log.info(
+      { chatId, hidden: pruned.hidden, freedTokens: pruned.freedTokens },
+      'inference: prune freed context budget',
+    );
+  }
+  if (pruned.freedTokens >= PRUNE_TRIGGER_TOKENS) {
+    // Prune handled it; skip the (expensive) summarize path.
+    return;
+  }
+
   await ctx.sql`UPDATE chats SET needs_compaction = true WHERE id = ${chatId}`;
   ctx.log.info({ chatId, promptTokens, completionTokens, contextLimit }, 'inference: flagged for compaction');
 }
diff --git a/apps/server/src/services/inference/prune.ts b/apps/server/src/services/inference/prune.ts
new file mode 100644
index 0000000..06d67c3
--- /dev/null
+++ b/apps/server/src/services/inference/prune.ts
@@ -0,0 +1,127 @@
+import type { Sql } from '../../db.js';
+
+// v1.13.4: two-tier compaction prune. Opencode's prune half (the cheap one);
+// summarize half shipped in v1.11.0 as services/compaction.ts.
+//
+// Algorithm: scan tool_result parts newest-first. Protect the last
+// PROTECTED_TOKENS of content (the model recently saw these — pruning them
+// kills coherence). Older parts are candidates. Mark them hidden_at only
+// if the candidate pool would free at least PRUNE_TRIGGER_TOKENS — pruning
+// 3 small tool_results to recover 500 tokens isn't worth the loss of
+// fidelity for the model's next turn.
+//
+// Stops at the last compaction summary boundary (chats.tail_start_id). The
+// v1.11.0 summary already encodes everything before that point; pruning
+// across the boundary would double-erase.
+
+export const PROTECTED_TOKENS = 40_000;
+export const PRUNE_TRIGGER_TOKENS = 20_000;
+
+// Rough char-to-token estimate. Same heuristic compaction's usable() uses
+// implicitly via the buffer constant.
+function estimateTokens(text: string): number {
+  return Math.ceil(text.length / 4);
+}
+
+function payloadTokens(payload: unknown): number {
+  return estimateTokens(JSON.stringify(payload ?? ''));
+}
+
+export interface PruneResult {
+  hidden: number;
+  freedTokens: number;
+}
+
+// Pure algorithmic core, exported for unit-test access. Takes parts already
+// ordered newest-first, plus an optional cutoff (last compaction summary
+// boundary). Returns the part ids to hide and the total token estimate of
+// the candidates. Caller does the DB UPDATE.
+export interface PartForPrune {
+  id: string;
+  payload: unknown;
+  created_at: Date;
+}
+
+export function selectPruneTargets(
+  partsNewestFirst: ReadonlyArray<PartForPrune>,
+  tailStartCreatedAt: Date | null,
+): { ids: string[]; freedTokens: number } {
+  let protectedTokens = 0;
+  const candidates: { id: string; tokens: number }[] = [];
+  let crossedProtection = false;
+
+  for (const part of partsNewestFirst) {
+    if (tailStartCreatedAt && part.created_at < tailStartCreatedAt) {
+      // Past the last summary boundary; the v1.11.0 anchored summary already
+      // covers everything older. Bail rather than double-erase.
+      break;
+    }
+    const tokens = payloadTokens(part.payload);
+    if (!crossedProtection) {
+      protectedTokens += tokens;
+      if (protectedTokens >= PROTECTED_TOKENS) {
+        crossedProtection = true;
+      }
+      continue;
+    }
+    candidates.push({ id: part.id, tokens });
+  }
+
+  const candidateTokens = candidates.reduce((s, c) => s + c.tokens, 0);
+  if (candidates.length === 0 || candidateTokens < PRUNE_TRIGGER_TOKENS) {
+    return { ids: [], freedTokens: 0 };
+  }
+  return { ids: candidates.map((c) => c.id), freedTokens: candidateTokens };
+}
+
+export async function prune(args: {
+  sql: Sql;
+  chatId: string;
+}): Promise<PruneResult> {
+  const { sql, chatId } = args;
+
+  // Newest-first scan of visible tool_result parts in this chat. Pull
+  // chats.tail_start_id alongside so we know where the last summary boundary
+  // sits (don't prune across it).
+  const parts = await sql<{
+    id: string;
+    payload: unknown;
+    created_at: Date;
+    tail_start_id: string | null;
+  }[]>`
+    SELECT p.id, p.payload, m.created_at,
+      (SELECT c.tail_start_id FROM chats c WHERE c.id = ${chatId}) AS tail_start_id
+    FROM message_parts p
+    JOIN messages m ON m.id = p.message_id
+    WHERE m.chat_id = ${chatId}
+      AND p.kind = 'tool_result'
+      AND p.hidden_at IS NULL
+    ORDER BY m.created_at DESC, p.sequence DESC
+  `;
+
+  if (parts.length === 0) {
+    return { hidden: 0, freedTokens: 0 };
+  }
+
+  // Read the boundary cutoff timestamp once. Older messages are off-limits.
+  let tailStartCreatedAt: Date | null = null;
+  const firstTailId = parts[0]?.tail_start_id ?? null;
+  if (firstTailId) {
+    const tailRow = await sql<{ created_at: Date }[]>`
+      SELECT created_at FROM messages WHERE id = ${firstTailId}
+    `;
+    tailStartCreatedAt = tailRow[0]?.created_at ?? null;
+  }
+
+  const decision = selectPruneTargets(parts, tailStartCreatedAt);
+  if (decision.ids.length === 0) {
+    return { hidden: 0, freedTokens: 0 };
+  }
+
+  await sql`
+    UPDATE message_parts
+    SET hidden_at = clock_timestamp()
+    WHERE id = ANY(${decision.ids})
+  `;
+  return { hidden: decision.ids.length, freedTokens: decision.freedTokens };
+}