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.

1 files changed, 63 insertions, 16 deletions

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') {