feat(mtconnect): serve DATA_SET/TABLE as compact JSON strings; park EVENT enumerations (#650)

Parser captures Entry/Cell content; the observation index merges /sample deltas
into the /current baseline (resetTriggered replaces, removed deletes, UNAVAILABLE
drops). Fixture gains a TABLE item and periodic DATA_SET/TABLE churn.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docs/drivers/MTConnect.md

@@ -103,8 +103,8 @@ request/response handshake — is a different mechanism and remains deferred; se
 | `TIME_SERIES` arrays (#627) | **Supported** as variable-length `double[]` (Float64 tags only) | [TIME_SERIES arrays](#time_series-arrays-627) |
 | One Agent client per driver, one `/raw` Device (#628) | **Enforced** (`MTConnectMultipleDevices` deploy error); multi-device Agents use several driver instances | [Known limitations](#known-limitations) |
 | Write-back (`IWritable`) | **Supported, off by default** (`Write.Enabled` + Agent `AllowPut`) | [Write-back](#write-back--observation-injection-off-by-default) |
-| EVENT controlled vocabularies as OPC UA enumerations | **Not supported** (stay String); not scheduled | See [Deferred](#deferred-not-in-this-build) |
-| `DATA_SET` / `TABLE` representations | **Not supported** - read as `BadNotSupported` | [Quality mapping](#quality-mapping) |
+| EVENT controlled vocabularies as OPC UA enumerations | **Parked / won't fix** (stay String) - see rationale | [EVENT enumerations](#event-enumerations-650-parked--wont-fix) |
+| `DATA_SET` / `TABLE` representations (#650) | **Supported** as a String carrying compact JSON | [DATA_SET / TABLE](#data_set--table-650) |
 | MTConnect Interfaces, SHDR ingest | Not built | [Deferred](#deferred-not-in-this-build) |
 
 **`IReadable.ReadAsync` is never called by the running server.** The
@@ -245,7 +245,7 @@ Other status codes an observation can surface:
 | `BadTypeMismatch` (`0x80740000`) | The Agent's text isn't a value of the tag's coerced type at all |
 | `BadOutOfRange` (`0x803C0000`) | The Agent reported a number the coerced type can't represent |
 | `BadDecodingError` (`0x80070000`) | A `TIME_SERIES` vector whose element count disagrees with the observation's own `sampleCount` (or the tag's fixed `ArrayDim`) — see [TIME_SERIES](#time_series-arrays-627) |
-| `BadNotSupported` (`0x803D0000`) | A shape this build doesn't materialize — a structured `DATA_SET`/`TABLE` observation (decided: stays unsupported, #627), or an array tag declared as anything other than Float64 |
+| `BadNotSupported` (`0x803D0000`) | A shape this build doesn't materialize — a `DATA_SET`/`TABLE` observation whose children are not `<Entry>` elements (a well-formed one is served as JSON since #650), or an array tag declared as anything other than Float64 |
 | `BadWaitingForInitialData` | Tag is authored but the Agent hasn't reported it yet |
 | `BadNodeIdUnknown` | DataItem id is neither authored nor ever observed |
 
@@ -272,8 +272,29 @@ in the Tag modal's array section).
 but the OPC UA node has no description/property slot through `DriverAttributeInfo`,
 and a sibling property node would need a new address-space mechanism. Decision:
 document it — the rate is a property of the Agent's DataItem (`sampleRate` in
-`/probe`), read it there. **`DATA_SET` / `TABLE` stay `BadNotSupported`** (decision, #627): they are
-key/value maps with no scalar or array OPC UA shape that preserves the keys.
+`/probe`), read it there.
+
+### DATA_SET / TABLE (#650)
+
+`DATA_SET` and `TABLE` observations carry their content in `<Entry key="…">` children (a `TABLE` entry holds
+`<Cell key="…">` children). They are served as a **String carrying compact, deterministic JSON** (OPC UA type
+String, never an array or structure - no new node shape, history/ACL/alarm paths unchanged; discovery and
+type inference already type these items String):
+
+- `DATA_SET` -> `{"offsetX":1.25,"toolNumber":7}`; `TABLE` -> `{"G54":{"X":1.0,"Y":2},"G55":{"X":3}}`.
+- Keys are ordinal-sorted at every level, no whitespace - the same content always serialises to the same
+  bytes, so value-dedup works. Values that are *strict JSON numbers* are emitted as numbers with their original
+  token (lossless: `1.0` stays `1.0`); anything else (`007`, `+5`, `on`) is a string.
+- **Merge semantics follow MTConnect 2.x.** A `/current` document states the *whole* set and **replaces** it;
+  a `/sample` chunk carries *deltas* that **merge** by key (a `TABLE` row is replaced as a unit by a later entry
+  for the same row key). An observation with `resetTriggered` replaces the accumulated set, and a
+  `resetTriggered` observation with no entries is the empty set `{}`. Several observations of one item in one
+  document fold in document order. The accumulated set is dropped on an Agent restart (`instanceId` change).
+- `removed="true"` deletes the key (or row): it is **absent** from the JSON, never `null`.
+- `UNAVAILABLE` is `BadNoCommunication` as for any observation, and also drops the accumulated set, so a
+  later delta cannot resurrect pre-outage entries.
+- An observation whose children are not `<Entry>` elements stays `BadNotSupported`. Writes to these items stay
+  refused (`WriteAsync` excludes them).
 
 ### Subscribe — the `/sample` pump
 
@@ -483,9 +504,13 @@ and records a state only when an alarm handler was attached to receive it. Conse
   unchanged triggers no re-subscribe, and needs none — the server-side carry-over covers it.
 - An alarm-only driver (no value tags) still runs the `/sample` pump.
 
-**EVENT controlled vocabularies as OPC UA enumerations — not built (parked, low priority).** EVENT values (`Execution`,
-`ControllerMode`, …) stay Strings carrying the Agent's own word; an enumeration would need a per-type
-vocabulary table that vendors extend freely.
+### EVENT enumerations (#650): parked / won't fix
+
+EVENT values (`Execution`, `ControllerMode`, …) stay Strings carrying the Agent's own word. Modelling them as
+OPC UA enumerations was considered and **declined**: the vocabulary is vendor-extensible, so it needs a per-type
+table plus an unknown-value fallback, a per-type enum node shape through discovery and raw-tag type inference,
+and it would break every consumer that reads these items as String (ScadaBridge) for little gain. Reopen only
+with an opt-in, tag-level `enumValues` design.
 
 ## Known limitations
 
@@ -563,9 +588,8 @@ for anything beyond values-and-conditions.
    pin the parsing rule itself.
 5. **A CONDITION alarm shows one condition per DataItem** — the most severe active `nativeCode`, not one
    Part 9 condition per code (see [CONDITION alarms](#condition-alarms-626)).
-6. **Structured `DATA_SET`/`TABLE` observations surface as
-   `BadNotSupported`**, not an approximation — see the Quality mapping table.
-   `TIME_SERIES` is served as `double[]` (#627, see
+6. **`DATA_SET`/`TABLE` observations are JSON Strings** (#650, see
+   [DATA_SET / TABLE](#data_set--table-650)); `TIME_SERIES` is served as `double[]` (#627, see
    [TIME_SERIES arrays](#time_series-arrays-627)); the sample rate is not
    surfaced on the node.
 
@@ -585,9 +609,8 @@ for anything beyond values-and-conditions.
 - **P1.5 fast-follow** (design
   [§9](../plans/2026-07-15-mtconnect-driver-design.md#9-phasing--effort)): CONDITION → native Part 9
   alarms **shipped** (#626, see [CONDITION alarms](#condition-alarms-626)); EVENT
-  controlled-vocabulary values → OPC UA enumerations is **not built** (EVENTs stay Strings), and
-  structured `DATA_SET`/`TABLE` observations stay `BadNotSupported`; both are tracked as a low-priority
-  follow-up, not part of P1.5.
+  controlled-vocabulary values → OPC UA enumerations is **parked / won't fix** (EVENTs stay Strings, #650);
+  `DATA_SET`/`TABLE` are served as JSON Strings (#650).
 - **P2 (on demand): SHDR adapter ingest.** A `SourceMode: "Agent" | "Shdr"`
   switch that opens the raw pipe-delimited SHDR TCP socket directly. Loses
   auto-discovery (no device model without an Agent in front, so