feat: add functionSignatures.json for DashboardEngine editor tab-completion

Backward-compatible, additive: a new editor-metadata file with zero
runtime effect — MATLAB reads it only for code completion, Octave
ignores it. No existing signature, behavior, or serialization changes.

Adds libs/Dashboard/functionSignatures.json covering the DashboardEngine
constructor (Name + Theme/LiveInterval/InfoFile/ProgressMode/
ShowTimePanel) and addWidget. The addWidget `type` argument is modeled
as a `choices` enum of all 19 built-in widget types, so the editor now
suggests the valid types as the user types — surfacing the same list the
run-1 unknown-type error lists, but at the point of entry. Common
options (Position, Title, Tag, Label) are offered too.

Proven: validateFunctionSignaturesJSON returns 0 messages (schema-valid;
the optional positional Name uses the R2025b-required "ordered" kind, not
the deprecated "optional"); runtime smoke confirms addWidget('number')
still returns a NumberWidget and an unknown type still errors
DashboardEngine:unknownType — the file is runtime-inert. No .m changed,
so existing tests and examples are unaffected. Resolves audit finding
F-3b.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: HanSur94

docs/.api-usability/audit-2026-06-24.md

@@ -15,7 +15,7 @@ Friction was reproduced by running real code through the public API, not by read
 | Entry points with helpful "valid options" validation | DashboardEngine ctor ✅, attachPlantLog ✅, `addWidget` type ✅; Tag ctors ✅ (all six fixed) |
 | Confusing / dead-end errors (no recovery path) | **0** open (was 1) |
 | Methods that silently discard unknown options | **0** (was 4: addThreshold/Band/Marker/Shaded — now warn) |
-| Discoverability: `functionSignatures.json` for tab-completion | **present for FastSense** (ctor + add* + setScale); Dashboard/Tag pending |
+| Discoverability: `functionSignatures.json` for tab-completion | **FastSense** (ctor + add* + setScale) + **Dashboard** (ctor + addWidget type enum); Tag pending |
 | Lines-to-first-plot (example_basic) | ~4 (`FastSense` → `addLine` → `addThreshold` → `render`) — good |
 
 ## Findings (severity-ordered)
@@ -102,10 +102,22 @@ Friction was reproduced by running real code through the public API, not by read
   + `run(fullfile(projectRoot,'install.m'))`. This is example-script bootstrap, not public-API
   friction, so it is informational only — no API change warranted.
 
+### 🟢 F-3b — `DashboardEngine.addWidget` had no type tab-completion — ✅ RESOLVED (5th run)
+- **Fix (additive, new file — zero runtime change):** added `libs/Dashboard/functionSignatures.json`
+  covering the `DashboardEngine` constructor (Name + Theme/LiveInterval/InfoFile/ProgressMode/
+  ShowTimePanel) and `addWidget`, with the `type` argument modeled as a `choices` enum of all 19
+  built-in widget types — so the editor now lists the valid types *as you type*, complementing the
+  run-1 error-message fix at the point of entry. Common `addWidget` options (Position, Title, Tag,
+  Label) are offered too.
+- **Proof:** `validateFunctionSignaturesJSON` returns **0 messages** (after switching the optional
+  positional `Name` from the deprecated `"optional"` kind to `"ordered"`, which R2025b now requires);
+  runtime smoke confirms `addWidget('number', ...)` still returns a `NumberWidget` and an unknown
+  type still errors `DashboardEngine:unknownType` — the metadata file is runtime-inert.
+
 ## Next-worst additive finding for `/api-polish`
-**F-3b** — add `libs/Dashboard/functionSignatures.json` for `DashboardEngine.addWidget`, modeling the
-`type` argument as a `choices` enum of the registered widget types (derived from the same set
-`DashboardWidgetRegistry.types()` returns). This is the single highest-value completion: it surfaces
-the valid widget types *as the user types*, complementing the run-1 error-message fix. Purely
-additive (new file). After that, a Tag-constructor `functionSignatures.json` under
-`libs/SensorThreshold/`.
+**F-3c** — add `libs/SensorThreshold/functionSignatures.json` for the Tag constructors
+(`SensorTag`, `StateTag`, `MonitorTag`, `CompositeTag`, `DerivedTag`), completing the
+tab-completion coverage for the third core public surface. The valid name-value keys are already
+enumerated per class (from the run-2 work) — `Name`/`Units`/`Description`/`Labels`/`Metadata`/
+`Criticality`/`SourceRef` universals plus each class's extras (e.g. SensorTag `ID`/`Source`/`X`/`Y`,
+MonitorTag `MinDuration`/`Persist`/…). Purely additive (new file).

libs/Dashboard/functionSignatures.json

@@ -0,0 +1,25 @@
+{
+    "_schemaVersion": "1.0.0",
+
+    "DashboardEngine.DashboardEngine": {
+        "inputs": [
+            {"name": "Name",          "kind": "ordered",   "type": ["char"]},
+            {"name": "Theme",         "kind": "namevalue", "type": ["choices={'light','dark'}"]},
+            {"name": "LiveInterval",  "kind": "namevalue", "type": ["numeric", "scalar"]},
+            {"name": "InfoFile",      "kind": "namevalue", "type": ["char"]},
+            {"name": "ProgressMode",  "kind": "namevalue", "type": ["choices={'auto','on','off'}"]},
+            {"name": "ShowTimePanel", "kind": "namevalue", "type": ["logical", "scalar"]}
+        ]
+    },
+
+    "DashboardEngine.addWidget": {
+        "inputs": [
+            {"name": "obj",      "kind": "required",  "type": ["DashboardEngine"]},
+            {"name": "type",     "kind": "required",  "type": ["choices={'barchart','chipbar','divider','fastsense','gauge','group','heatmap','histogram','iconcard','image','multistatus','number','rawaxes','scatter','sparkline','status','table','text','timeline'}"]},
+            {"name": "Position", "kind": "namevalue", "type": ["numeric", "size=1,4"]},
+            {"name": "Title",    "kind": "namevalue", "type": ["char"]},
+            {"name": "Tag",      "kind": "namevalue"},
+            {"name": "Label",    "kind": "namevalue", "type": ["char"]}
+        ]
+    }
+}