plugin: announce DocumentOpened once per load, not per tab switch

The guard remembered only the last announced (tab, generation), so
switching A -> B -> A announced A's load again. Each tab now carries
its own pending flag, set when a document is installed and cleared by
the boundary dispatch.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plugin-host-model-completion-plan.md

@@ -427,8 +427,8 @@ and `SelectionChanged` (the plain selection set) at the fingerprint-guarded mess
 the v4 bridge already uses (`notify_plugins_selection_changed` / `notify_plugins_document_changed`,
 plus the automation post-op boundary), and a new additive `DocumentOpened { tab_id }` variant
 (discriminant 10, the counterpart of the existing `DocumentTabClosed`) that fires once per whole
-document install — file open, template new, system open — keyed on a new per-tab document
-generation. Boundary rule: dispatch happens after the mutation settles and pending history scopes
+document install — file open, template new, system open — keyed on a per-tab pending flag, so
+neither an edit nor a tab switch repeats it. Boundary rule: dispatch happens after the mutation settles and pending history scopes
 closed, never mid-undo/mid-pick, and history (undo/redo) replay itself emits nothing — the
 boundary is the only channel; plugin-initiated writes publish immediately after settling, like
 the drawing-changed event, with the boundary fingerprint deduplicating. Handlers may call HostApi

src/app/automation.rs

@@ -729,8 +729,8 @@ impl OpenCADStudio {
                 // The headless session starts on the welcome (Start) tab, which
                 // blocks drawing commands; turn it into a real drawing.
                 self.tabs[i].is_start = false;
-                // A fresh document became resident (API v9): mint a new
-                // generation so the post-op boundary announces `DocumentOpened`.
+                // A fresh document became resident (API v9): the post-op
+                // boundary announces `DocumentOpened`.
                 self.tabs[i].note_document_loaded();
                 self.entity_summary()
             }
@@ -770,9 +770,8 @@ impl OpenCADStudio {
                         self.tabs[i].current_path = Some(path_buf);
                         self.tabs[i].is_start = false;
                         self.tabs[i].scene.rebuild_derived_caches();
-                        // The opened document settled (API v9): mint a new
-                        // generation so the post-op boundary announces
-                        // `DocumentOpened` once for this load.
+                        // The opened document settled (API v9): the post-op
+                        // boundary announces `DocumentOpened` once for this load.
                         self.tabs[i].note_document_loaded();
                         let mut summary = self.entity_summary();
                         if dropped > 0 {
@@ -1855,7 +1854,7 @@ mod tests {
             "a new document announces exactly one open: {log:?}"
         );
 
-        // A follow-up op does not repeat it: generation-keyed dispatch.
+        // A follow-up op does not repeat it: the tab's pending flag cleared.
         app.automation_op(r#"{"op":"query","type":"Line"}"#);
         let log = plugin_dispatch_log();
         assert!(
@@ -1917,7 +1916,7 @@ mod tests {
         // The next message boundary does not repeat it.
         app.notify_plugins_document_opened();
         let log = plugin_dispatch_log();
-        assert_eq!(log.len(), 0, "generation-keyed dispatch dedupes: {log:?}");
+        assert_eq!(log.len(), 0, "the pending flag dedupes: {log:?}");
         let _ = std::fs::remove_file(&path);
     }
 

src/app/control/sheets.rs

@@ -466,8 +466,8 @@ impl OpenCADStudio {
         self.tabs[i].current_path = None;
         self.tabs[i].is_start = false;
         self.tabs[i].dirty = true;
-        // A whole document just became resident in the tab (API v9): mint a
-        // fresh generation so the boundary announces `DocumentOpened` once.
+        // A whole document just became resident in the tab (API v9): the
+        // boundary announces `DocumentOpened` once.
         self.tabs[i].note_document_loaded();
         Ok(purged)
     }

src/app/document.rs

@@ -18,17 +18,6 @@ use std::sync::Arc;
 
 static NEXT_DOCUMENT_TAB_ID: AtomicU64 = AtomicU64::new(1);
 
-/// Monotonic source for `DocumentTab::document_generation` (API v9): every
-/// minted value is process-unique, so any freshly installed document — file
-/// open, template new, system open — differs from every generation a plugin
-/// has been told about, and the opened-notification guard fires exactly once
-/// per load.
-static NEXT_DOCUMENT_GENERATION: AtomicU64 = AtomicU64::new(1);
-
-fn next_document_generation() -> u64 {
-    NEXT_DOCUMENT_GENERATION.fetch_add(1, Ordering::Relaxed)
-}
-
 // ── Dynamic input ──────────────────────────────────────────────────────────
 
 /// One quantity shown in the dynamic-input overlay near the cursor.
@@ -158,13 +147,12 @@ pub(super) struct DocumentTab {
     /// Monotonic committed-edit/undo/redo revision. Background save completion
     /// uses it with scene epochs so an older snapshot never clears newer work.
     pub(super) edit_revision: u64,
-    /// Monotonic identity of the document currently resident in this tab: a
-    /// fresh value is minted whenever a whole document replaces the tab's
-    /// content (file open, template new, system open), and edits leave it
-    /// alone. The plugin-opened notification guard
-    /// (`OpenCADStudio::notify_plugins_document_opened`, API v9) keys on it
-    /// so `DocumentOpened` dispatches exactly once per load.
-    pub(super) document_generation: u64,
+    /// A whole document replaced this tab's content (file open, template new,
+    /// system open) and native plugins have not been told yet: the
+    /// message boundary (`OpenCADStudio::notify_plugins_document_opened`,
+    /// API v9) dispatches `DocumentOpened` once and clears it, so edits and
+    /// switching between tabs never announce the same load again.
+    pub(super) document_opened_pending: bool,
     pub(super) tab_title: String,
     pub(super) properties: PropertiesPanel,
     pub(super) layers: LayerPanel,
@@ -648,7 +636,7 @@ impl DocumentTab {
             dirty: false,
             recovery_save_as_required: false,
             edit_revision: 0,
-            document_generation: next_document_generation(),
+            document_opened_pending: true,
             prev_selection: Vec::new(),
             tab_title: format!("Drawing{}", n),
             properties: PropertiesPanel::empty(),
@@ -723,11 +711,11 @@ impl DocumentTab {
     }
 
     /// A whole document just replaced this tab's content (file open, template
-    /// new, system open): mint a fresh generation so the message-boundary
-    /// dispatch announces `DocumentOpened` exactly once for this load (API
-    /// v9). Call after the document and its derived caches have settled.
+    /// new, system open): the next message boundary announces
+    /// `DocumentOpened` once for this load (API v9). Call after the document
+    /// and its derived caches have settled.
     pub(super) fn note_document_loaded(&mut self) {
-        self.document_generation = next_document_generation();
+        self.document_opened_pending = true;
     }
 
     pub(super) fn tab_display_name(&self) -> String {

src/app/mod.rs

@@ -1153,12 +1153,6 @@ pub(super) struct OpenCADStudio {
     /// boundaries as well as after plugin-initiated writes.
     #[cfg(not(target_arch = "wasm32"))]
     last_plugin_document: Option<(u64, u64)>,
-    /// `(tab id, document generation)` last dispatched as `DocumentOpened` —
-    /// a tab's generation changes only when a whole document replaced its
-    /// content, so the opened notification fires once per load, never per
-    /// edit (API v9).
-    #[cfg(not(target_arch = "wasm32"))]
-    last_plugin_document_opened: Option<(u64, u64)>,
     /// External add-on packages found in the plugins folder, refreshed when the
     /// Plugin Manager opens.
     external_plugins: Vec<crate::plugin::external::ExternalPlugin>,
@@ -4838,8 +4832,6 @@ impl OpenCADStudio {
             last_plugin_selection: None,
             #[cfg(not(target_arch = "wasm32"))]
             last_plugin_document: None,
-            #[cfg(not(target_arch = "wasm32"))]
-            last_plugin_document_opened: None,
             external_plugins: Vec::new(),
             loaded_plugin_ids: rustc_hash::FxHashSet::default(),
             plugin_load_errors: rustc_hash::FxHashMap::default(),

src/app/update/file.rs

@@ -2276,9 +2276,9 @@ impl OpenCADStudio {
                 .set(crate::app::OPEN_PHASE_FINALIZING, 10000, 1, 1);
         }
         self.opening.take();
-        // The document and its derived caches have settled: mark the tab's
-        // generation so the next message boundary announces `DocumentOpened`
-        // to native plugins exactly once for this load (API v9).
+        // The document and its derived caches have settled: the next message
+        // boundary announces `DocumentOpened` to native plugins exactly once
+        // for this load (API v9).
         self.tabs[i].note_document_loaded();
         // The tab list just changed (and the active tab with it): remember
         // it for the next boot's restore flow (web session memory).

src/app/update/mod.rs

@@ -344,9 +344,9 @@ impl OpenCADStudio {
 
     /// Announce that a whole document became resident in the active tab —
     /// opened from file, created from a template, or loaded by a system open
-    /// (API v9). Keyed on `(tab id, document generation)`, which changes only
-    /// when a tab's content is wholesale replaced, so an edit can never fire
-    /// it twice and a reload fires it exactly once. Part of the same
+    /// (API v9). Each tab carries its own pending flag, set only when its
+    /// content is wholesale replaced, so neither an edit nor a tab switch can
+    /// fire it twice and a reload fires it exactly once. Part of the same
     /// post-message boundary as the selection and document dispatches: runs
     /// after the mutation settles and pending history scopes closed, never
     /// inside history replay or interactive picking.
@@ -359,11 +359,9 @@ impl OpenCADStudio {
         if self.tabs[i].is_start {
             return;
         }
-        let key = (self.tabs[i].id, self.tabs[i].document_generation);
-        if self.last_plugin_document_opened == Some(key) {
+        if !std::mem::take(&mut self.tabs[i].document_opened_pending) {
             return;
         }
-        self.last_plugin_document_opened = Some(key);
         crate::plugin::v4_support::publish_document_opened(self.tabs[i].id);
     }