fix(newos4): world_model_query default path parses again (v4.6.83-84)

_modelDigest() returned JSON.stringify(...) cut at 4000 chars plus '…(digest truncated)'. The
tool then did JSON.parse() on it, so the default detail threw 'Unexpected end of JSON input'
every single call; detail:'full' worked only because it returned the object untouched.

The digest now returns an OBJECT (_modelSnapshot) and shrinks by reducing list lengths, then by
dropping whole sections with an explicit 'omitted' list. The string form is generated at the
edge and is always valid JSON.

Verified: default call -> no error, 13-key snapshot, facts answered; caps 400/1200/4000 all under
cap and parseable; the residual floor at cap 200 is identity fields only.

1 files changed, 32 insertions, 9 deletions

diff --git a/modules/core/module-world-model.js b/modules/core/module-world-model.js
index d48327b..54a17e4 100644
--- a/modules/core/module-world-model.js
+++ b/modules/core/module-world-model.js
@@ -446,30 +446,53 @@ class WorldModelModule {
     // 2026-10-21: ask() used to be a keyword table only, so any real question got
     // "Unknown query". Whitelist the fields we are willing to send to a model
     // (never the raw model object: it is persisted alongside other VFS data).
-    _modelDigest(maxChars) {
+    // v4.6.83: the digest used to be a JSON string cut at 4000 chars with '…(digest truncated)'
+    // glued on. Every caller that tried to parse it got "Unexpected end of JSON input" — the
+    // world_model_query tool did exactly that on its default path. A digest must shrink, never
+    // break: this returns a valid OBJECT and the string form is only produced at the edge.
+    _modelSnapshot(maxChars) {
         const m = this._model;
-        if (!m) return '';
+        if (!m) return null;
         const cap = maxChars || 4000;
-        const pick = {
+        const build = (keep) => ({
             version: m.version,
             synthesized: m.synthesized,
             system: m.system,
             modules: m.modules,
             files: m.files,
-            skills: { count: m.skills && m.skills.count, skills: ((m.skills && m.skills.skills) || []).slice(0, 40) },
+            skills: { count: m.skills && m.skills.count, skills: ((m.skills && m.skills.skills) || []).slice(0, keep) },
             memory: m.memory,
             agents: m.agents,
             telemetry: m.telemetry,
             projects: m.projects,
-            recent: (m.recent || []).slice(0, 20),
+            recent: (m.recent || []).slice(0, Math.min(keep, 20)),
             // 2026-10-21: the model only ever exposed a COUNT ("9 recent errors") with no detail,
             // so neither the user nor the LLM could say what failed. Carry the last few.
             recentErrorSample: this._errorSample ? this._errorSample() : [],
             changesSinceLastSnapshot: this._diffSincePrev ? this._diffSincePrev() : []
-        };
-        let json = JSON.stringify(pick);
-        if (json.length > cap) json = json.slice(0, cap) + '…(digest truncated)';
-        return json;
+        });
+        // Shrink the lists until the snapshot fits. Truncating the JSON text is what broke it.
+        for (const keep of [40, 20, 10, 5, 3, 1, 0]) {
+            const pick = build(keep);
+            if (JSON.stringify(pick).length <= cap) return pick;
+        }
+        // Last resort: drop whole sections, in order of least value, until it fits. Still a
+        // valid object — a caller can always JSON.parse it and see what was left out.
+        const lean = build(0);
+        lean.truncated = true;
+        lean.omitted = [];
+        for (const key of ['changesSinceLastSnapshot', 'recentErrorSample', 'recent', 'projects',
+                           'skills', 'agents', 'files', 'modules', 'telemetry', 'memory']) {
+            if (JSON.stringify(lean).length <= cap) break;
+            if (key in lean) { delete lean[key]; lean.omitted.push(key); }
+        }
+        return lean;
+    }
+
+    // String form, for prompts. Always valid JSON now.
+    _modelDigest(maxChars) {
+        const snap = this._modelSnapshot(maxChars);
+        return snap ? JSON.stringify(snap) : '';
     }
 
     // Last few tool/agent errors with their tool name, for the digest (bounded).