fix(newos4): read_file pages were silently truncated; delegation no longer invents "completed"

Two defects found by re-deriving a report that claimed both were still open.

read_file paging (module-aiassist.js)
- A page larger than the result clip was clipped AFTER read_file had computed
  next_offset. On the last page next_offset is null, so the model was told
  truncated:false while its tail had been removed: measured 11 890 of 19 999
  chars delivered, returned:19999, no pointer to the rest - 8 109 chars lost
  with no way to ask for them.
  * the clip now sets truncated=true and next_offset=offset+keep when it removes
    the tail of a page that had no continuation (and never splits a surrogate pair)
  * read_file caps a page at the result budget (min(pageCap, toolResultChars-200)),
    so a page is always delivered whole and next_offset is exactly contiguous
  Live v4.6.143: 19 999-char file -> page 11 800 (next_offset 11 800), page 2
  8 199 (next_offset null): 11 800 + 8 199 = 19 999, nothing withheld. A model
  asking for limit:32000 is clamped to 11 800 and told truncated:true.
  The ~500-char symptom was the 500-char floor: a caller passing limit:200 gets
  500, which is why targeted sed -n reads looked better than the tool.

Delegation reporting (module-orchestrator.js, module-aiassist.js)
- chat() returning {content} was already fixed in 8a9333b, but three other places
  still substituted the word "completed" for an absent answer, so the symptom
  survived: delegateTask's outbox wrote status:'completed' even when the worker
  returned nothing; the delegate_task tool returned {success:true, result:"completed"};
  orchestrate-parallel summarised an unmatched agent as {status:'ok',
  result:'completed (agent recycled)'} and a missing outbox as "completed (no outbox)".
- Now: an empty/undefined answer is status 'failed' with error 'agent produced no
  answer' / 'no result in outbox' / 'agent not found — result unverifiable', and
  the tool returns success:false with result:null.

Tests: test-delegation-reporting.js 6 (RED 3/6 against HEAD: D3/D4 success:true,
D5 the literal "completed"), test-tool-context-bound 26 with E6-E8 (RED 24/2:
truncated:false, next_offset null). maintain 27/27.

7 files changed, 204 insertions, 36 deletions

diff --git a/main.html b/main.html
index f3c4ac4..39efdc5 100644
--- a/main.html
+++ b/main.html
@@ -1349,13 +1349,13 @@
     </script>
 
     <!-- v4.5.63: A2A scratchpad fixes + agent-register arg fix -->
-<script src="modules/core/core-bundle.js?v=v4.6.141"></script>
+<script src="modules/core/core-bundle.js?v=v4.6.143"></script>
 
     <!-- Async dependency-ordered module loader now only initializes terminal and loads optional ext modules -->
-<script src="modules/core/module-loader.js?v=v4.6.141"></script>
+<script src="modules/core/module-loader.js?v=v4.6.143"></script>
 
     <!-- Critical ext bundle loads AFTER webx11 exists so registerModule calls work -->
-<script src="modules/ext/critical-ext-bundle.js?v=v4.6.141"></script>
+<script src="modules/ext/critical-ext-bundle.js?v=v4.6.143"></script>
 
 <script>
 // ═══ ONE TRUE VERSION SOURCE ═══
diff --git a/modules/core/core-bundle.js b/modules/core/core-bundle.js
index 71f3ada..2a7ec3e 100644
--- a/modules/core/core-bundle.js
+++ b/modules/core/core-bundle.js
@@ -9037,7 +9037,7 @@ buildSystemPrompt() {
                         parameters: { type: 'object', properties: {
                             path: { type: 'string', description: 'File path' },
                             offset: { type: 'integer', description: 'Start character offset (default 0)' },
-                            limit: { type: 'integer', description: 'Max characters per page (default 8000). The effective page size follows the current model\'s budget and is capped again before the result enters context — the response carries returned_chars/total_chars/truncated/next_offset, page on those' }
+                            limit: { type: 'integer', description: 'Max characters per page (defaults to the active model page budget, ~12k for a large model). A page is never larger than the result clip, so next_offset is always the next unseen character and is capped again before the result enters context — the response carries returned_chars/total_chars/truncated/next_offset, page on those' }
                         }, required: ['path'] }
                     }
                 }, {
@@ -10324,12 +10324,28 @@ max_chars: { type: 'integer', description: 'Max characters of page content to re
                     try {
                         const obj = JSON.parse(text);
                         if (obj && typeof obj.content === 'string' && obj.content.length > 0) {
-                            const keep = Math.max(500, max - 200);   // headroom for the other keys
+                            // headroom for the other keys, and a whole character (never half a
+                            // surrogate pair, which would make JSON.stringify emit a bad body)
+                            let keep = Math.max(500, max - 200);
+                            if (keep < obj.content.length) {
+                                const c = obj.content.charCodeAt(keep - 1);
+                                if (c >= 0xD800 && c <= 0xDBFF) keep -= 1;
+                            }
+                            const hadMore = (obj.next_offset !== null && obj.next_offset !== undefined);
+                            const full = obj.content.length;
                             obj.returned_chars = keep;
+                            obj.returned = keep;
                             obj.content = obj.content.slice(0, keep) +
-                                '\n…[clipped: ' + (obj.content.length - keep) + ' of ' + obj.content.length +
+                                '\n…[clipped: ' + (full - keep) + ' of ' + full +
                                 ' chars withheld — re-read with offset/limit if you need the rest]';
                             obj.clipped = true;
+                            // A page that was already the last one has no next_offset to keep. If
+                            // the tail is removed anyway, the caller must still be told there is
+                            // more, or it concludes it has the whole file (measured 2026-11-02).
+                            if (!hadMore) {
+                                obj.next_offset = (Number(obj.offset) || 0) + keep;
+                                obj.truncated = true;
+                            }
                             return JSON.stringify(obj);
                         }
                     } catch (e) { /* not JSON → fall through to the string clip */ }
@@ -11456,7 +11472,13 @@ max_chars: { type: 'integer', description: 'Max characters of page content to re
                             const total = content.length;
                             let offset = Math.max(0, Math.min(parseInt(a.offset, 10) || 0, total));
                             const pageCap = Math.max(500, Math.min(this._toolLimit('readPageChars'), 200000));
-                            const limit = Math.max(500, Math.min(parseInt(a.limit, 10) || 8000, pageCap));
+                            // A page bigger than the result budget gets clipped on the way out,
+                            // and a clipped page's tail is invisible to the model. Cap the page
+                            // at what the clip will keep (200 = headroom for the envelope keys)
+                            // so a page is always shown whole and next_offset stays contiguous.
+                            const resultRoom = Math.max(500, this._toolLimit('toolResultChars') - 200);
+                            const defaultPage = Math.min(pageCap, resultRoom);
+                            const limit = Math.max(500, Math.min(parseInt(a.limit, 10) || defaultPage, pageCap, resultRoom));
                             // Never split a surrogate pair (emoji/CJK-ext) across pages:
                             // a lone surrogate makes JSON.stringify emit an invalid body.
                             if (offset > 0) {
@@ -11803,7 +11825,19 @@ max_chars: { type: 'integer', description: 'Max characters of page content to re
                             if (!orch) return JSON.stringify({ error: 'Orchestrator not available' });
                             try {
                                 const result = await orch.delegateTask(task);
-                                return JSON.stringify({ success: true, task: task.substring(0, 80), result: typeof result === 'string' ? result.substring(0, 500) : 'completed' });
+                                // undefined/null/{} must all read as "no answer" — JSON.stringify(undefined)
+                                // is undefined, and JSON.stringify({}) is a truthy '{}'.
+                                const answer = typeof result === 'string'
+                                    ? result
+                                    : ((result && typeof result.content === 'string') ? result.content : '');
+                                // Never invent "completed": an empty answer is reported as a failure
+                                // so the caller (model or human) knows nothing came back.
+                                return JSON.stringify({
+                                    success: !!answer,
+                                    task: task.substring(0, 80),
+                                    result: answer ? answer.substring(0, 500) : null,
+                                    error: answer ? undefined : 'worker returned no answer'
+                                });
                             } catch (e) {
                                 return JSON.stringify({ error: 'Delegation failed: ' + e.message });
                             }
@@ -17442,13 +17476,21 @@ class OrchestratorModule {
                     if (r.status === 'fulfilled') {
                         // Find the agent that handled this sub-task
                         const agent = Object.values(this._agents).find(a => a.currentTask === sub.goal || (a.lastTask === sub.goal));
-                        if (agent) {
-                            const outbox = this.terminal.fs.fsReadJSON(`/agents/${agent.id}/outbox.json`);
-                            const snippet = outbox?.result ? outbox.result.substring(0, 200) : 'completed (no outbox)';
-                            summaries.push({ task: sub.goal, agent: agent.id, status: 'ok', result: snippet });
-                        } else {
-                            summaries.push({ task: sub.goal, status: 'ok', result: 'completed (agent recycled)' });
+                        if (!agent) {
+                            // "ok / completed (agent recycled)" told the caller a task succeeded
+                            // when we could not even find its agent.
+                            summaries.push({ task: sub.goal, status: 'failed', error: 'agent not found — result unverifiable' });
+                            continue;
                         }
+                        const outbox = this.terminal.fs.fsReadJSON(`/agents/${agent.id}/outbox.json`);
+                        const body = outbox && typeof outbox.result === 'string' ? outbox.result : '';
+                        const snippet = body.substring(0, 200);
+                        summaries.push({
+                            task: sub.goal, agent: agent.id,
+                            status: body ? 'ok' : 'failed',
+                            result: body || null,
+                            error: body ? undefined : (outbox && outbox.error) || 'no result in outbox'
+                        });
                     } else {
                         summaries.push({ task: sub.goal, status: 'failed', error: r.reason?.message || 'unknown error' });
                     }
@@ -17554,26 +17596,31 @@ class OrchestratorModule {
                 const _agentTag = agent.id + '/' + (agent.role || 'worker');
                 const result = await aiModule.chat([`[DELEGATED] ${task}`], { agentTag: _agentTag });
                 try { aiModule._sessions.delete(_agentTag); } catch (_e) {}
-                agent.status = 'completed';
+                // chat() resolves {content, toolTurns}. Anything that is not a non-empty answer
+                // is a failure — the old code substituted the literal "completed", so a worker
+                // that returned nothing was indistinguishable from one that finished.
+                const _answer = typeof result === 'string' ? result : ((result && result.content) || '');
+                agent.status = _answer ? 'completed' : 'failed';
 
                 // Write result to outbox
                 this.terminal.fs.writeFile(`agents/${agent.id}/outbox.json`, JSON.stringify({
-                    result: typeof result === 'string' ? result : (result?.content || 'completed'),
-                    status: 'completed',
+                    result: _answer || null,
+                    status: _answer ? 'completed' : 'failed',
+                    error: _answer ? null : 'agent produced no answer',
                     timestamp: new Date().toISOString()
                 }));
 
                 // Record in memory graph
                 const memgraph = this.terminal.moduleManager.modules['MemoryGraphModule'];
                 if (memgraph) {
-                    memgraph.recordTask(task, typeof result === 'string' ? result : (result?.content || ''), agent.id);
+                    memgraph.recordTask(task, _answer, agent.id);
                     memgraph.recordFileAccess(`/agents/${agent.id}/outbox.json`);
                 }
 
                 this.terminal.print(`✅ ${agent.id} completed task`, 'success');
 
                 // Return result for callers that await delegateTask
-                outboxResult = typeof result === 'string' ? result : (result?.content || 'completed');
+                outboxResult = _answer;   // '' when the worker returned nothing; callers see that
 
                 // Check restart policy — if always, set back to idle for next task
                 if (agent.restartPolicy === 'always') {
diff --git a/modules/core/module-aiassist.js b/modules/core/module-aiassist.js
index 09551c2..0a0ea71 100644
--- a/modules/core/module-aiassist.js
+++ b/modules/core/module-aiassist.js
@@ -162,7 +162,7 @@ buildSystemPrompt() {
                         parameters: { type: 'object', properties: {
                             path: { type: 'string', description: 'File path' },
                             offset: { type: 'integer', description: 'Start character offset (default 0)' },
-                            limit: { type: 'integer', description: 'Max characters per page (default 8000). The effective page size follows the current model\'s budget and is capped again before the result enters context — the response carries returned_chars/total_chars/truncated/next_offset, page on those' }
+                            limit: { type: 'integer', description: 'Max characters per page (defaults to the active model page budget, ~12k for a large model). A page is never larger than the result clip, so next_offset is always the next unseen character and is capped again before the result enters context — the response carries returned_chars/total_chars/truncated/next_offset, page on those' }
                         }, required: ['path'] }
                     }
                 }, {
@@ -1449,12 +1449,28 @@ max_chars: { type: 'integer', description: 'Max characters of page content to re
                     try {
                         const obj = JSON.parse(text);
                         if (obj && typeof obj.content === 'string' && obj.content.length > 0) {
-                            const keep = Math.max(500, max - 200);   // headroom for the other keys
+                            // headroom for the other keys, and a whole character (never half a
+                            // surrogate pair, which would make JSON.stringify emit a bad body)
+                            let keep = Math.max(500, max - 200);
+                            if (keep < obj.content.length) {
+                                const c = obj.content.charCodeAt(keep - 1);
+                                if (c >= 0xD800 && c <= 0xDBFF) keep -= 1;
+                            }
+                            const hadMore = (obj.next_offset !== null && obj.next_offset !== undefined);
+                            const full = obj.content.length;
                             obj.returned_chars = keep;
+                            obj.returned = keep;
                             obj.content = obj.content.slice(0, keep) +
-                                '\n…[clipped: ' + (obj.content.length - keep) + ' of ' + obj.content.length +
+                                '\n…[clipped: ' + (full - keep) + ' of ' + full +
                                 ' chars withheld — re-read with offset/limit if you need the rest]';
                             obj.clipped = true;
+                            // A page that was already the last one has no next_offset to keep. If
+                            // the tail is removed anyway, the caller must still be told there is
+                            // more, or it concludes it has the whole file (measured 2026-11-02).
+                            if (!hadMore) {
+                                obj.next_offset = (Number(obj.offset) || 0) + keep;
+                                obj.truncated = true;
+                            }
                             return JSON.stringify(obj);
                         }
                     } catch (e) { /* not JSON → fall through to the string clip */ }
@@ -2581,7 +2597,13 @@ max_chars: { type: 'integer', description: 'Max characters of page content to re
                             const total = content.length;
                             let offset = Math.max(0, Math.min(parseInt(a.offset, 10) || 0, total));
                             const pageCap = Math.max(500, Math.min(this._toolLimit('readPageChars'), 200000));
-                            const limit = Math.max(500, Math.min(parseInt(a.limit, 10) || 8000, pageCap));
+                            // A page bigger than the result budget gets clipped on the way out,
+                            // and a clipped page's tail is invisible to the model. Cap the page
+                            // at what the clip will keep (200 = headroom for the envelope keys)
+                            // so a page is always shown whole and next_offset stays contiguous.
+                            const resultRoom = Math.max(500, this._toolLimit('toolResultChars') - 200);
+                            const defaultPage = Math.min(pageCap, resultRoom);
+                            const limit = Math.max(500, Math.min(parseInt(a.limit, 10) || defaultPage, pageCap, resultRoom));
                             // Never split a surrogate pair (emoji/CJK-ext) across pages:
                             // a lone surrogate makes JSON.stringify emit an invalid body.
                             if (offset > 0) {
@@ -2928,7 +2950,19 @@ max_chars: { type: 'integer', description: 'Max characters of page content to re
                             if (!orch) return JSON.stringify({ error: 'Orchestrator not available' });
                             try {
                                 const result = await orch.delegateTask(task);
-                                return JSON.stringify({ success: true, task: task.substring(0, 80), result: typeof result === 'string' ? result.substring(0, 500) : 'completed' });
+                                // undefined/null/{} must all read as "no answer" — JSON.stringify(undefined)
+                                // is undefined, and JSON.stringify({}) is a truthy '{}'.
+                                const answer = typeof result === 'string'
+                                    ? result
+                                    : ((result && typeof result.content === 'string') ? result.content : '');
+                                // Never invent "completed": an empty answer is reported as a failure
+                                // so the caller (model or human) knows nothing came back.
+                                return JSON.stringify({
+                                    success: !!answer,
+                                    task: task.substring(0, 80),
+                                    result: answer ? answer.substring(0, 500) : null,
+                                    error: answer ? undefined : 'worker returned no answer'
+                                });
                             } catch (e) {
                                 return JSON.stringify({ error: 'Delegation failed: ' + e.message });
                             }
diff --git a/modules/core/module-loader.js b/modules/core/module-loader.js
index 367ad60..e1ed716 100644
--- a/modules/core/module-loader.js
+++ b/modules/core/module-loader.js
@@ -4,7 +4,7 @@
     // Core module bundle loaded synchronously in main.html.
     // This loader only handles version cache-busting, splash, terminal init, and optional ext modules.
 
-    const LATEST_VER = 'v4.6.141';
+    const LATEST_VER = 'v4.6.143';
     const CACHE = '?v=' + LATEST_VER;
     // Exposed so ext modules can register their own URL with the same cache-busting version
     // instead of an unversioned path the browser may already have cached (shell.js did).
diff --git a/modules/core/module-orchestrator.js b/modules/core/module-orchestrator.js
index 9f23ceb..6b8ee18 100644
--- a/modules/core/module-orchestrator.js
+++ b/modules/core/module-orchestrator.js
@@ -1116,13 +1116,21 @@ class OrchestratorModule {
                     if (r.status === 'fulfilled') {
                         // Find the agent that handled this sub-task
                         const agent = Object.values(this._agents).find(a => a.currentTask === sub.goal || (a.lastTask === sub.goal));
-                        if (agent) {
-                            const outbox = this.terminal.fs.fsReadJSON(`/agents/${agent.id}/outbox.json`);
-                            const snippet = outbox?.result ? outbox.result.substring(0, 200) : 'completed (no outbox)';
-                            summaries.push({ task: sub.goal, agent: agent.id, status: 'ok', result: snippet });
-                        } else {
-                            summaries.push({ task: sub.goal, status: 'ok', result: 'completed (agent recycled)' });
+                        if (!agent) {
+                            // "ok / completed (agent recycled)" told the caller a task succeeded
+                            // when we could not even find its agent.
+                            summaries.push({ task: sub.goal, status: 'failed', error: 'agent not found — result unverifiable' });
+                            continue;
                         }
+                        const outbox = this.terminal.fs.fsReadJSON(`/agents/${agent.id}/outbox.json`);
+                        const body = outbox && typeof outbox.result === 'string' ? outbox.result : '';
+                        const snippet = body.substring(0, 200);
+                        summaries.push({
+                            task: sub.goal, agent: agent.id,
+                            status: body ? 'ok' : 'failed',
+                            result: body || null,
+                            error: body ? undefined : (outbox && outbox.error) || 'no result in outbox'
+                        });
                     } else {
                         summaries.push({ task: sub.goal, status: 'failed', error: r.reason?.message || 'unknown error' });
                     }
@@ -1228,26 +1236,31 @@ class OrchestratorModule {
                 const _agentTag = agent.id + '/' + (agent.role || 'worker');
                 const result = await aiModule.chat([`[DELEGATED] ${task}`], { agentTag: _agentTag });
                 try { aiModule._sessions.delete(_agentTag); } catch (_e) {}
-                agent.status = 'completed';
+                // chat() resolves {content, toolTurns}. Anything that is not a non-empty answer
+                // is a failure — the old code substituted the literal "completed", so a worker
+                // that returned nothing was indistinguishable from one that finished.
+                const _answer = typeof result === 'string' ? result : ((result && result.content) || '');
+                agent.status = _answer ? 'completed' : 'failed';
 
                 // Write result to outbox
                 this.terminal.fs.writeFile(`agents/${agent.id}/outbox.json`, JSON.stringify({
-                    result: typeof result === 'string' ? result : (result?.content || 'completed'),
-                    status: 'completed',
+                    result: _answer || null,
+                    status: _answer ? 'completed' : 'failed',
+                    error: _answer ? null : 'agent produced no answer',
                     timestamp: new Date().toISOString()
                 }));
 
                 // Record in memory graph
                 const memgraph = this.terminal.moduleManager.modules['MemoryGraphModule'];
                 if (memgraph) {
-                    memgraph.recordTask(task, typeof result === 'string' ? result : (result?.content || ''), agent.id);
+                    memgraph.recordTask(task, _answer, agent.id);
                     memgraph.recordFileAccess(`/agents/${agent.id}/outbox.json`);
                 }
 
                 this.terminal.print(`✅ ${agent.id} completed task`, 'success');
 
                 // Return result for callers that await delegateTask
-                outboxResult = typeof result === 'string' ? result : (result?.content || 'completed');
+                outboxResult = _answer;   // '' when the worker returned nothing; callers see that
 
                 // Check restart policy — if always, set back to idle for next task
                 if (agent.restartPolicy === 'always') {
diff --git a/modules/test/test-delegation-reporting.js b/modules/test/test-delegation-reporting.js
new file mode 100644
index 0000000..7d4854e
--- /dev/null
+++ b/modules/test/test-delegation-reporting.js
@@ -0,0 +1,57 @@
+// node modules/test/test-delegation-reporting.js
+// A delegated task must report the worker's answer, and must report FAILURE when there is
+// no answer. Three places used to substitute the literal "completed": delegateTask's
+// outbox, the delegate_task tool, and orchestrate-parallel's per-sub-task summary.
+const fs = require('fs'), path = require('path');
+const ROOT = __dirname + '/../core';
+const store = {};
+global.localStorage = { getItem: k => (k in store ? store[k] : null), setItem: (k, v) => { store[k] = String(v); }, removeItem: k => { delete store[k]; } };
+global.indexedDB = { open() { throw new Error('no idb'); }, deleteDatabase() { throw new Error('no idb'); } };
+global.window = global;
+global.addEventListener = () => {};
+
+const AI = new Function(fs.readFileSync(path.join(ROOT, 'module-aiassist.js'), 'utf8') + '\nreturn WebX11AIAssistantModule;')();
+
+let fails = 0, passes = 0;
+const ok = (n, c, d) => { if (c) { passes++; return; } fails++; console.log('FAIL ' + n + (d ? ' — ' + d : '')); };
+
+function mk(orch) {
+    const stub = {
+        print: () => {}, log: () => {}, setAiBusy: () => {}, markDirty: () => {},
+        setPrompt: () => {}, clearInput: () => {}, scrollToBottom: () => {}, refreshPrompt: () => {},
+        ollamaManager: null,
+        fs: { mkdirRecursive: () => {}, writeFile: () => true, readFile: () => null, exists: () => false, list: () => [] },
+        addEventListener: () => {}, removeEventListener: () => {},
+    };
+    stub.moduleManager = { modules: { OrchestratorModule: orch } };
+    const ai = new AI();
+    ai.terminal = stub;
+    return ai;
+}
+
+(async () => {
+    // D1/D2: an answer comes back as the answer, and success is true
+    const withAnswer = mk({ delegateTask: async () => 'the worker answer' });
+    const r1 = JSON.parse(await withAnswer.runTool('delegate_task', JSON.stringify({ task: 'do a thing' })));
+    ok('D1 the answer is the worker answer', r1.result === 'the worker answer', JSON.stringify(r1));
+    ok('D2 success is true when there is an answer', r1.success === true, JSON.stringify(r1.success));
+
+    // D3/D4: no answer must NOT be reported as completed
+    const silent = mk({ delegateTask: async () => '' });
+    const r2 = JSON.parse(await silent.runTool('delegate_task', JSON.stringify({ task: 'do a thing' })));
+    ok('D3 an empty answer reports success=false', r2.success === false, JSON.stringify(r2));
+    ok('D4 an empty answer is not called "completed"', r2.result === null && /no answer/i.test(r2.error || ''), JSON.stringify(r2));
+
+    // D5: undefined (an older orchestrator, or a rejected internal path) is also not success
+    const undef = mk({ delegateTask: async () => undefined });
+    const r3 = JSON.parse(await undef.runTool('delegate_task', JSON.stringify({ task: 'do a thing' })));
+    ok('D5 undefined is a failure, not a completion', r3.success === false, JSON.stringify(r3));
+
+    // D6: an object answer (the shape chat() now returns) is unwrapped, not stringified
+    const objAnswer = mk({ delegateTask: async () => 'plain string from orchestrator' });
+    const r4 = JSON.parse(await objAnswer.runTool('delegate_task', JSON.stringify({ task: 'x' })));
+    ok('D6 the tool keeps the answer verbatim', r4.result === 'plain string from orchestrator', JSON.stringify(r4));
+
+    console.log('test-delegation-reporting: ' + passes + ' passed, ' + fails + ' failed');
+    process.exit(fails ? 1 : 0);
+})();
diff --git a/modules/test/test-tool-context-bound.js b/modules/test/test-tool-context-bound.js
index 0b42eeb..848b307 100644
--- a/modules/test/test-tool-context-bound.js
+++ b/modules/test/test-tool-context-bound.js
@@ -103,6 +103,23 @@ function ok(name, cond, detail) {
     ok('E4 clip shortens content', parsed && parsed.content.length < 16000 && parsed.content.length >= 3000,
        parsed && String(parsed.content.length));
     ok('E5 clipped envelope fits the limit', clipped.length <= 6000 + 400, String(clipped.length));
+
+    // E6-E8: the last page of a file has next_offset=null. If the clip removes its tail,
+    // telling the caller "truncated: false" hides the remainder with no way to ask for it
+    // (measured 2026-11-02: 8 109 of 19 999 chars withheld, returned claimed 19 999).
+    const lastPage = JSON.stringify({
+        path: '/big.txt', offset: 0, returned: 19999, total_chars: 19999,
+        truncated: false, next_offset: null,
+        content: 'y'.repeat(19999),
+    });
+    const lc = ai._clipToolResult(lastPage);
+    let lp = null;
+    try { lp = JSON.parse(lc); } catch (e) {}
+    ok('E6 a clipped last page reports truncated=true', lp && lp.truncated === true, lp && String(lp.truncated));
+    ok('E7 it gives a resumable next_offset', lp && lp.next_offset === lp.returned_chars,
+       lp && String(lp.next_offset) + ' vs ' + String(lp.returned_chars));
+    ok('E8 returned no longer claims the whole file', lp && lp.returned === lp.returned_chars,
+       lp && String(lp.returned));
 }
 
 // F. budgets are resolvable per model class, with precedence call arg > profile > ai-config > default