feat(scripts): read-only, allow-listed Files global for site scripts; Delmia test receiver parses recipe files

Script file access (design docs/plans/2026-09-28-script-file-access-design.md): Files.ReadTextAsync /
ReadLinesAsync / ExistsAsync on site ScriptGlobals (+ Instance.Files), backed by the site-singleton
ScriptFileReader. The one host-mediated exception to the System.IO ban - scripts still never name a
System.IO type. OFF by default: ScadaBridge:SiteRuntime:ScriptFileAccess:AllowedRoots (empty = every call
throws Disabled) + MaxFileBytes (1 MiB, validated 1..64 MiB, roots must be absolute). Guard: fully
qualified, no device paths / ADS, canonical path strictly inside a root (directory-boundary match), no
reparse point on the file or any directory below the root, size cap before and during the read.
Errors are one Commons type, ScriptFileAccessException(+ScriptFileAccessFailure); Commons.Types.Scripts
joins the default script imports on every surface so it binds by short name. Mirrored on
ScriptCompileSurface (CompileFiles, parity-pinned) and the Test Run sandbox (binds, refuses Disabled).
Inbound (central) scripts do not get it.

Rig: docker/recipes (sample RecipeValueName,RecipeValue files incl. an invalid one) bind-mounted
read-only at /app/recipes on both site-a nodes with AllowedRoots [/app/recipes]. The TestMesMachine
SimDelmiaRecipe simulator now reads + parses the downloaded file, converts each value to its recipe tag's
type and loads it all-or-nothing (14 new TestDelmiaReceiver attributes); verify-mes-test-machine.sh
group A covers accept / re-download / invalid lines / NotFound / OutsideAllowedRoots, VERIFY_GROUPS
selects groups (rig: AD).

docs/requirements/Component-SiteRuntime.md

@@ -520,6 +520,17 @@ Available to all script runs and alarm on-trigger runs:
 - The type lives in Commons so the runtime accessor and the Script Analysis compile-only surface (`ScriptCompileSurface.CompileAlarmsAccessor`) project to the **same** type — a script binding at the design-time gate binds identically at the site. Parity is pinned by `CompileSurfaceParityTests`.
 - Design record: `docs/plans/2026-06-30-mes-alarm-status-api.md` §5.2.
 
+### File Access (`Files`, read-only, allow-listed — 2026-09-28)
+- `Files.ReadTextAsync(path)` → `string`, `Files.ReadLinesAsync(path)` → `IReadOnlyList<string>` (`\r\n`/`\n`/`\r`; a trailing line break adds no empty last line), `Files.ExistsAsync(path)` → `bool`. Also reachable as `Instance.Files`. The use case that motivated it: a recipe/NC file whose path a Delmia/MES call hands to the machine, which a script parses and loads into attributes.
+- **The one sanctioned exception to the `System.IO` ban, and it is host-mediated.** Scripts still cannot name any `System.IO` type — the trust policy is unchanged. The runtime `FilesAccessor` delegates to the site-singleton `ScriptFileReader` (`SiteRuntime/Scripts/`), which does every check on the host side.
+- **Off by default.** `ScadaBridge:SiteRuntime:ScriptFileAccess:AllowedRoots` (list of absolute local/UNC directories, default empty) enables it; with no roots every call throws `ScriptFileAccessException(Disabled)`, so an unconfigured site behaves exactly as before. `ScriptFileAccess:MaxFileBytes` (default 1 MiB, validated 1…64 MiB) caps one read. Both validated at boot (`SiteRuntimeOptionsValidator` — a relative root is rejected). Read per call through `IOptionsMonitor`.
+- **Guard, in order:** roots configured → path non-empty, fully qualified, not a device path (`\\?\`, `\\.\`), no NTFS alternate data stream → canonical path (`Path.GetFullPath`, so `..` is resolved first) **strictly inside** a root with a directory-boundary match (root `C:\recipes` does not admit `C:\recipes2\x`, and the root itself is not a file) → no symbolic link / junction / reparse point on the file **or on any directory between the root and the file** (the root itself may be a link — an administrator chose it) → size under the cap, re-checked while reading in case the file grows. Files are opened `FileShare.ReadWrite | Delete` so a file still being written by its producer can be read; text is BOM-detected, UTF-8 by default.
+- **Errors are one Commons type.** Every refusal and I/O failure is `ScriptFileAccessException` (`Commons.Types.Scripts`) with a `Failure` of `Disabled`, `InvalidPath`, `OutsideAllowedRoots`, `LinkNotAllowed`, `NotFound`, `TooLarge` or `IoError` — scripts cannot name `System.IO` exception types, so this is what they `catch`. `Commons.Types.Scripts` is now one of the **default script imports** on every surface (runtime, deploy gate, Test Run editor), so the short name binds.
+- **Bounded by the run.** Reads are cancelled by the script's own execution deadline as well as any token the script passes. Refusals (outside roots, links) log a Warning on the node; successful reads log at Debug. There is no audit row — file reads are not an audited channel (the `AuditLog` scope is outbound API/DB, notifications and inbound API).
+- **The node's service account still needs read permission** on the path; the allow-list only ever narrows access. A time-of-check/time-of-use window exists between the link check and the open (a writer inside an allowed root could swap a file for a link in between) — acceptable because only the directories an administrator lists are reachable at all, and read-only.
+- **Site scripts only.** Inbound API method scripts (central) have no `Files` global. The Central UI Test Run sandbox mirrors the member so scripts bind, but every call throws `ScriptFileAccessException(Disabled)` — central cannot reach a site's filesystem — so a script's own error handling runs as it would on an unconfigured site. The design-time `ScriptCompileSurface.CompileFiles` mirror is pinned by `CompileSurfaceParityTests`.
+- Design record: `docs/plans/2026-09-28-script-file-access-design.md`.
+
 ### Logging (`Log`)
 - `Log.Debug(message, exception?)` / `Log.Info` / `Log.Warn` / `Log.Error` — leveled, per-run logging available to **every** script, alongside the `Alarms` accessor above (design `docs/plans/2026-09-09-flow-debugger-step-logs-design.md` D4/D5). Synchronous, `void`, and it **never throws into the script**: a failing sink is swallowed, because a debug observer must not fail a production run.
 - **Every line always reaches the node's `ILogger`** (structured `Instance` / `Script` / `ExecutionId` / message), traced or not — an untraced run is an ordinary logging surface and pays nothing else. A `ScriptTrace` / `ScriptLog` **audit row** is emitted **only when the run is traced** (a Flow Debugger Live run, or a real call to a method with `TraceAllCalls`), so a timer or value-change script logging at high rate costs no audit volume. There is no site-event-log sink for `Log.*`.