Scripts: an error in code an earlier #targetengine run compiled names that run's file and line

A function an earlier run of a named engine defined was reported without
a line, column or file when it threw in a later run. The realm now gives
each source a tag that stays the same from run to run (Realm::error_tag,
Realm::script_tag), and no two sources share one once the tags run out.
Each named engine keeps the source maps of its runs' scripts, included
files and $.evalFile files, within 8 MiB, dropping the oldest first, and
an error in kept code is reported at that file, line and column. The
report's name and the console line keep the calling run's name. For an
earlier script given as source, file is that run's name.

Docs: docs/mcp.md (Script engines), script.run params text,
docs/target-app-parity.md.

docs/mcp.md

@@ -1873,8 +1873,13 @@ no engines, and the engines it left are dropped when their own thread next uses
   and the other eight are kept. Each named engine has a heap of 64 MiB, which holds what it keeps between runs; a run
   that goes past it ends with the heap limit, and the engine stays usable.
 - The documents go back after an uncaught error, a limit or `script.stop` as they do for any run, and the engine keeps
-  the globals the run set before it ended. An internal error drops the engine. An error in a function an earlier run
-  defined is reported without a line and column.
+  the globals the run set before it ended. An internal error drops the engine.
+- An error in code an earlier run compiled, such as a function it defined, is reported at that code's line and column
+  in the earlier run's script, a file it included or a file its `$.evalFile` ran, and the report's `file` names that
+  file. For an earlier script given as `source`, `file` is that run's name. The report's `name` and the console line's
+  name stay the calling run's, as in `caller.js: /path/lib.jsx:12:5: Error: kept`. Each engine keeps these places
+  for 8 MiB of source maps, the oldest going first; an error in code whose place is gone, or in code that `eval` or
+  `Function` compiled, is reported without a line and column, and the code still runs.
 - `vc`, `$`, `alert`, `confirm` and `prompt` act for the run that calls them, including a copy an earlier run kept in a
   global. `vc.args` is the calling run's `args`, through a `vc` object an earlier run kept too. An engine
   holds no document: `vc.document` is a copy, read when it is called. What a run sets on `$` (`$.locale`,

docs/target-app-parity.md

@@ -756,6 +756,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - Scripts: an error a `finally` block passes on is still reported where it was thrown when the block's allocations collect garbage under a small heap limit, and a `finally` block that `return`, `break` or `continue` leaves drops the saved location of its error as it leaves, so a collection no longer counts that code as live. VectorCraft's own rule. `crates/js/src/host_tests.rs`.
   - Scripts: a run reads its preprocessor lines before any of it runs: `#include` and `//@include` put another file in place of the line, looked for beside the including file, in the `#includepath` folders and in `JSINCLUDE`; `#script` names the run; `#target` and `#strict off` are taken, `#strict on` turns on strict write checks (below), `#targetengine` names the engine (below), and `#engine` is refused. `$.evalFile` runs a file with the same globals and returns its last value, and `$.fileName` and `$.includePath` give the file being run and the include folders. A script run from a file reads these files only in its folder and below, without `..` names or links that lead out, and an error in one is reported at its own file, line and column ([preprocessor directives](https://extendscript.docsforadobe.dev/extendscript-tools-features/preprocessor-directives/), [the `$` object](https://extendscript.docsforadobe.dev/extendscript-tools-features/dollar-object/); `crates/engine/src/tests/script_include.rs`).
   - Scripts: `#targetengine name` (and `//@targetengine name`) runs the script in a named engine that lasts for the session, and a later script that names it sees the globals and functions earlier ones left ([preprocessor directives](https://extendscript.docsforadobe.dev/extendscript-tools-features/preprocessor-directives/)); `$.engineName` gives the name ([the `$` object](https://extendscript.docsforadobe.dev/extendscript-tools-features/dollar-object/)). VectorCraft's own rules: a script without the line and `#targetengine main` get a new engine each run, the line comes once in the script itself before its code, a session keeps 8 named engines with 64 MiB of heap each, an error or a stop keeps the globals the run set while the documents go back, kept host functions act for the run that calls them, `script.engines` lists the engines and `script.engine.drop` drops one, and the web build has none. `crates/engine/src/tests/script_engines.rs`.
+  - Scripts: a runtime error is shown at the line that was running ([the help page](https://extendscript.docsforadobe.dev/extendscript-toolkit/debugging-in-the-toolkit/)). VectorCraft's own rules: an error in code an earlier run of a named engine compiled, such as a function it defined, is reported at that code's file, line and column (the earlier run's script, a file it included or a file its `$.evalFile` ran), while the report and its console line keep the calling run's name; a script given as text is named by its run's name, and each engine keeps these places for 8 MiB of source maps, the oldest going first. `crates/engine/src/tests/script_engines.rs`.
   - Scripts: `File` and `Folder` ([File object](https://extendscript.docsforadobe.dev/file-system-access/file-object/), [Folder object](https://extendscript.docsforadobe.dev/file-system-access/folder-object/)) name files and folders by platform or URI path, with `name`, `fsName`, `absoluteURI`, `relativeURI`, `parent`, `Folder.current` and `encode`/`decode`, and read them: `exists`, `length`, the dates, `getFiles` with a mask or a function, and `open('r')` with `read`, `readln`, `readch`, `seek`, `tell` and `close`, decoding by byte order mark, `encoding`, UTF-8 or CP1252. VectorCraft's own rules: a script reads only in its own folder and below (and inside the automation read roots when they are set); any other path and a network or device path are refused before anything is looked up, and a link that leads out is refused as well (`false` or `null`, with `error` set); a file is read whole up to 8 MiB and a run reads up to 32 MiB; writing, the file dialogs and `execute` are not available yet. `crates/engine/src/tests/script_io.rs`.
   - Scripts: `#strict on` (and `//@strict on`) runs the script with the checks the [`$` object](https://extendscript.docsforadobe.dev/extendscript-tools-features/dollar-object/) help page gives for `$.strict`: an assignment to a read-only property throws a `TypeError`, and so does a new property on an object that takes none. VectorCraft's own rules: a getter-only property counts as read-only, the objects that take no new properties are the non-extensible ones (`Object.preventExtensions`, `seal`, `freeze`, and the frozen `vc` and `$` objects), the last `#strict` line of the script and its includes sets the whole run, a file `$.evalFile` runs keeps its own line's checks for its code, and the rest of ES5 strict mode stays with `'use strict'`. Without the line, runs are unchanged. `crates/engine/src/tests/script_include.rs` (`strict_on_*`, `strict_mode_in_eval_file_is_scoped`), `crates/js/src/interp_tests.rs` (`strict_writes_are_separate_from_es5_strict`).
   - Scripts folder: File › Scripts lists the `.js` and `.jsx` files of the `Scripts` folder next to the preferences, each named after its file without the extension, with each subfolder as a submenu, above Check Script… and Other Script… (https://helpx.adobe.com/illustrator/desktop/automate-visualize-data/automate-actions/install-and-run-scripts.html). VectorCraft's own rules: the folder is read again when the window becomes active and when the File menu opens (in the macOS menu bar, when any of its menus opens, and the new listing shows the next time the menu opens), links are not followed, and one read stops at 2,048 entries, 512 scripts, 128 subfolders, 4 levels or 250 ms. `script.listInstalled` returns the listing. `crates/engine/src/tests/script_folder.rs`, `crates/ui-egui/src/tests/scripts_menu.rs`.