feat: convert script handling to pocos

docs/advanced-filemaker-scripting-syntax.md

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+# Advanced FileMaker Scripting Syntax
+
+Status: authoritative reference for all script-step POCOs.
+
+## Purpose
+
+SharpFM renders FileMaker script XML as editable display text. Some XML
+state doesn't naturally appear in FileMaker Pro's own display (object
+IDs, flags, embedded newlines, etc.). To round-trip that state faithfully
+through display-text editing, SharpFM extends FM Pro's display grammar
+with a small set of named conventions — collectively, **Advanced
+FileMaker Scripting Syntax**.
+
+The extensions are safe because **FileMaker Pro never consumes SharpFM's
+display text**. FM Pro reads only the binary `Mac-XMSS` clipboard
+payload; `POCO.ToXml()` always emits pure FM Pro XML regardless of
+whatever extensions are present in the display. The display text is a
+SharpFM-internal surface for user editing, and our display parser only
+ever reads our own extended output.
+
+## Core invariant
+
+> `ToDisplayLine()` and `FromDisplayParams()` together are lossless for
+> every piece of state the POCO carries. XML state that is dropped is
+> dropped because it carries no information, not because the display
+> can't express it.
+
+Every POCO's docstring contains a **zero-loss audit** (see below) that
+enumerates XML state explicitly and marks each item as either rendered
+by FM Pro natively, covered by an advanced-syntax extension, or
+intentionally dropped with a written rationale.
+
+## The three extension forms
+
+Pick the form that matches the shape of the hidden state:
+
+| Shape of state | Syntax | Example | Used for |
+|---|---|---|---|
+| Id annotation on a named reference | `(#id)` suffix after the name | `"Find Customer" (#7)` | Script, Layout, TableOccurrence, Field id round-trip |
+| Boolean / enum flag already in FM Pro's grammar | word token inline, matching FM Pro's wording | `Exit after last: On` | Flags FM Pro itself renders; we mirror its wording |
+| Bulk invisible state (multi-slot / structured) | trailing `; Kind: [...]` block, word-token values | `; Buttons: ["OK" commit; "Cancel" nocommit]` | Button configurations, input-field metadata, any future bulk state |
+
+### Form 1 — `(#id)` suffix
+
+Appended to a quoted or `Table::Field` name:
+
+- `FieldRef` emits `People::FirstName (#7)` when an id is known; plain
+  `People::FirstName` otherwise.
+- `PerformScriptStep` emits `"Find Customer" (#42)`.
+- `GoToLayoutStep` emits `"Invoices Detail" (#11)`.
+
+Omitted when the id is zero or unknown — `(#0)` would be visual noise
+for unresolved references.
+
+### Form 2 — inline word tokens
+
+Parsed at a specific named prefix, matching FM Pro's own rendering of
+the same flag:
+
+- `Exit after last: On` on found-set iterators.
+- `With dialog: Off` on steps that can suppress their confirmation UI.
+- `Restore: On|Off` — **reserved**. Not currently emitted by any POCO;
+  see "What to drop vs. surface" below for the rationale.
+
+### Form 3 — trailing `; Kind: [...]` blocks
+
+Bulk or structured state that doesn't reduce to a single flag:
+
+- `; Buttons: ["OK" commit; "Cancel" nocommit; "" nocommit]` — used by
+  Show Custom Dialog for its button configuration.
+- Future bulk state (Input Field specs, etc.) takes this form.
+
+## Parsing precedence
+
+Named-prefix inline tokens (Form 2) are parsed before trailing
+`Kind: [...]` blocks (Form 3). A display line like
+
+```
+Go to Record/Request/Page [ Next ; Exit after last: On ; Buttons: [...] ]
+```
+
+is tokenized as:
+1. Positional `Next` (Form 2 equivalent — fixed-position enum).
+2. Named inline `Exit after last: On` (Form 2).
+3. Named block `Buttons: [...]` (Form 3).
+
+Form 1 (`(#id)`) is applied inside each name-bearing token — e.g. inside
+the bracketed name-and-id of a named ref — and does not collide with
+Form 2 or Form 3 separators.
+
+## Zero-loss audit requirement
+
+Every POCO author must complete this audit in the class XML doc
+comment. Template:
+
+```
+/// <summary>
+/// Zero-loss audit for StepName:
+/// <list type="bullet">
+///   <item>&lt;Step&gt; attributes (enable/id/name) — round-tripped.</item>
+///   <item>&lt;Calculation&gt; CDATA — round-tripped via Calculation.</item>
+///   <item>&lt;SomeElement state="..."/&gt; — Form 2 token "Some: On|Off".</item>
+///   <item>&lt;Dropped/&gt; — intentionally dropped; rationale: ...</item>
+/// </list>
+/// </summary>
+```
+
+Items fall into exactly one of these buckets:
+
+1. **Rendered natively by FM Pro** — FM Pro's display grammar already
+   covers it; SharpFM mirrors the wording.
+2. **Covered by an extension form** — one of the three above.
+3. **Intentionally dropped** — rationale required. See next section for
+   how to judge.
+
+Omitting the audit is a review blocker.
+
+## What to drop vs. surface
+
+Hidden state is surfaced only when a user could meaningfully change it.
+Some state is structurally present in XML but semantically fixed — FM
+Pro never alters it, never emits it in clipboard output, and no user
+workflow produces a different value. Round-tripping such state adds
+visual noise for zero information.
+
+### Canonical drop: `<Restore state="False"/>` on `If`
+
+Upstream `agentic-fm` snippets include the element; FM Pro's own
+clipboard output never does; no FM Pro user interaction produces
+`state="True"`. `IfStep` drops it on both read and write. The audit
+entry documents the drop:
+
+> &lt;Restore state="False"/&gt; — intentionally dropped. FM Pro never
+> changes the value and never emits the element in clipboard output; it
+> carries no information worth round-tripping.
+
+### Canonical surface: field `id` via `(#id)` suffix
+
+`<Field table="T" id="12" name="F"/>` is a real identity — the id
+selects which field is referenced, and two fields named `F` in different
+tables are not interchangeable. Dropping the id would change semantics.
+`FieldRef` always emits `(#12)` when an id is available.
+
+### The heuristic
+
+- If two valid FM Pro script states would be visually identical under
+  the display grammar without the extension, **surface** the state.
+- If the state has a fixed value that no user can change, **drop** it.
+- If you're not sure which, **surface**. Reversing a surface → drop
+  later is non-breaking; reversing a drop → surface may break tests
+  users wrote against the earlier display.
+
+## Adjacent convention: `//` disabled-step prefix
+
+Disabled steps are prefixed with `//` in display text:
+
+```
+// Set Error Capture [ On ]
+```
+
+Parsing strips the `//` and sets `ScriptStep.Enabled = false`. This is
+a document-level convention (applied to any step line) rather than a
+per-step extension. Covered here for completeness.
+
+## Implementation touch points
+
+- `FieldRef.ToDisplayString` / `FieldRef.FromDisplayToken`
+  (`src/SharpFM.Model/Scripting/Values/FieldRef.cs`) — Form 1 reference
+  implementation.
+- `CommentStep.ReturnGlyph`
+  (`src/SharpFM.Model/Scripting/Steps/CommentStep.cs`) — the `⏎`
+  (U+23CE) glyph for single-line rendering of multi-line comment text.
+  An idiom adjacent to the three forms but specific to Comment.
+- `ScriptLineParser.ParseLine`
+  (`src/SharpFM.Model/Scripting/ScriptLineParser.cs`) — disabled-step
+  prefix and bracket tokenization.
+- `PerformScriptStep.FromDisplayParams`,
+  `GoToLayoutStep.FromDisplayParams` — Form 1 regex parsers for named
+  refs with `(#id)` suffixes.
+
+## Change log
+
+- **2026-04** — Extracted from `docs/step-definitions.md:44-69` into
+  its own document as part of the POCO big-bang migration. Rationale
+  section ("what to drop vs. surface") added with `Restore` on `If` as
+  the canonical drop example.