feat(messaging): balanced TOOL parsing, DM shorthand, box.exec, tools.list

- response-harvester: extract [TOOL]/[EXEC] JSON args with balanced-brace
  scanning (']' and nesting inside args no longer truncate calls); add
  [DM {...}] shorthand mapping to dm.send; native aliases (dm, box,
  tools) plus arg-synonym normalization; formatters and expanded hints.
- exec-constrained: new read-only box.exec op (27 allowlisted box-ctl
  reads) and tools.list op backed by --list-ops for dynamic discovery.
- prompt_envelope: advertise dm.send/box.exec/tools.list in every timer
  DM; add dm_call builder.
- lookup_engine + regex_patterns.json: canonical tool_call pattern
  accepts the DM engine, ']' in args, one nesting level.
- tests/test_tool_calls.py: 38 tests; docs/INBAND-MESSAGING-SPEC.md:
  accepted decision record (Final).

lookup_internal/regex_patterns.json

@@ -99,18 +99,20 @@
     },
     "tool_call": {
       "name": "In-Band Tool Execution Call",
-      "pattern": "\\[(?P<engine>TOOL|EXEC)\\s+(?P<op>[a-zA-Z0-9_.-]+)\\s+(?P<args>\\{.*?\\})\\]",
+      "pattern": "\\[(?P<engine>TOOL|EXEC|DM)\\s+(?:(?P<op>[a-zA-Z0-9_.-]+)\\s+)?(?P<args>\\{([^{}]|\\{[^{}]*\\})*\\})\\]",
       "flags": ["DOTALL"],
-      "description": "Matches synthesized inline tool execution directives with JSON arguments.",
+      "description": "Matches inline tool directives with JSON args (one nesting level; response-harvester.py scans balanced braces for arbitrary depth). DM carries no op (implies dm.send).",
       "named_groups": {
-        "engine": "Either TOOL or EXEC",
-        "op": "Target operation name (e.g. followup.create, swarm.spawn)",
-        "args": "Valid JSON string of argument parameters"
+        "engine": "TOOL, EXEC, or DM (DM implies dm.send)",
+        "op": "Target operation (e.g. followup.create, swarm.spawn); absent for DM",
+        "args": "JSON argument object; may contain ']' and one level of nested objects"
       },
       "test_samples": {
         "valid": [
           "[TOOL followup.create {\"in_m\": 5, \"prompt\": \"check\"}]",
-          "[EXEC health.check {\"verbose\": true}]"
+          "[EXEC health.check {\"verbose\": true}]",
+          "[TOOL box.exec {\"action\": \"job-get\", \"arg\": \"a-b[0]\"}]",
+          "[DM {\"to\": \"pip\", \"target\": \"pip tasks\", \"message\": \"hi\"}]"
         ],
         "invalid": [
           "[TOOL followup.create without args]",