diff --git a/apps/fieldcraft-web/src/web.rs b/apps/fieldcraft-web/src/web.rs
index dab0f37..5dda3f9 100644
--- a/apps/fieldcraft-web/src/web.rs
+++ b/apps/fieldcraft-web/src/web.rs
@@ -190,6 +190,8 @@ fn services(inbox: Inbox, ctx: egui::Context) -> Services {
         recent_path: None,
         // Preferences last for the page's run.
         prefs_path: None,
+        // egui opens links itself in the browser.
+        open_url: None,
     }
 }
 
diff --git a/apps/fieldcraft/src/main.rs b/apps/fieldcraft/src/main.rs
index 9d1d8af..df9e10a 100644
--- a/apps/fieldcraft/src/main.rs
+++ b/apps/fieldcraft/src/main.rs
@@ -13,8 +13,8 @@
 
 mod control_server;
 
-use fieldcraft_engine::Session;
 use fieldcraft_engine::autosave::{self, Autosaver};
+use fieldcraft_engine::{Session, crash, logfile};
 use fieldcraft_ui_egui::{Filter, ModelApp, Services};
 
 const USAGE: &str =
@@ -47,6 +47,8 @@ struct App {
     autosaver: Option<Autosaver>,
     /// App time of the last autosave check.
     autosaved_at: f64,
+    /// The first frame was drawn (the crash journal says the app is up).
+    running: bool,
 }
 
 impl App {
@@ -61,6 +63,10 @@ impl App {
 
 impl eframe::App for App {
     fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        if !self.running {
+            self.running = true;
+            crash::activity("running");
+        }
         self.app.logic(ctx);
         if self.app.now - self.autosaved_at >= AUTOSAVE_SECONDS {
             self.autosaved_at = self.app.now;
@@ -76,6 +82,8 @@ impl eframe::App for App {
         {
             log::warn!("autosave: {e}");
         }
+        log::info!("FieldCraft closed");
+        crash::end_session();
     }
     fn raw_input_hook(&mut self, _ctx: &egui::Context, raw: &mut egui::RawInput) {
         self.app.raw_input_hook(raw);
@@ -96,9 +104,55 @@ fn services() -> Services {
         // Beside the recovery folder in the per-user data folder.
         recent_path: fieldcraft_io::recovery::default_dir().and_then(|d| d.parent().map(|p| p.join("recent.json"))),
         prefs_path: fieldcraft_io::recovery::default_dir().and_then(|d| d.parent().map(|p| p.join("prefs.json"))),
+        open_url: Some(Box::new(open_url)),
     }
 }
 
+/// Open a web link in the default browser, with the system's own opener: `open` (macOS),
+/// `xdg-open` (Linux and the BSDs), `explorer` (Windows). The link is one argument, never
+/// passed through a shell. Only https links are opened.
+fn open_url(url: &str) -> Result<(), String> {
+    if !url.starts_with("https://") {
+        return Err(format!("not a web link: {}", url.chars().take(80).collect::<String>()));
+    }
+    let opener = if cfg!(target_os = "macos") {
+        "open"
+    } else if cfg!(windows) {
+        "explorer"
+    } else {
+        "xdg-open"
+    };
+    let mut child = std::process::Command::new(opener).arg(url).spawn().map_err(|e| format!("{opener}: {e}"))?;
+    // Reaped off the window thread; its exit status says nothing (`explorer` exits with 1 even
+    // when it opened the link).
+    std::thread::spawn(move || {
+        let _ = child.wait();
+    });
+    Ok(())
+}
+
+/// Crash reports and the log file (docs/crash-reports.md): reports of earlier runs that crashed
+/// come back, for the window to offer. Both live in the app's data folder (a temporary one in
+/// runs driven by automation); `FIELDCRAFT_CRASH_DIR` moves the crash folder.
+fn start_reporting() -> Vec<crash::Summary> {
+    // First the crash reports: an unclean exit's report takes the dead run's lines from the log.
+    let crashed = crash::default_dir().map(|dir| crash::install(dir, crash::Build::current())).unwrap_or_default();
+    match fieldcraft_io::recovery::data_dir().map(|d| logfile::install(&d.join("logs"), log::LevelFilter::Info)) {
+        Some(Ok(path)) => eprintln!("fieldcraft: log {}", path.display()),
+        Some(Err(e)) => eprintln!("fieldcraft: no log file: {e}"),
+        None => {}
+    }
+    let b = crash::Build::current();
+    log::info!(
+        "FieldCraft {} started ({}), crash reports in {}",
+        b.version,
+        b.version_line(),
+        crash::default_dir().map(|d| d.display().to_string()).unwrap_or_default()
+    );
+    crash::activity("startup");
+    crashed
+}
+
 /// Command-line options.
 #[derive(Debug, Default, PartialEq)]
 struct Args {
@@ -152,9 +206,10 @@ fn main() -> eframe::Result {
     };
     if args.control.is_some() {
         // A run driven by automation keeps its autosaves (and recent files and preferences, which
-        // live beside them) in a temporary folder, never the user's.
+        // live beside them), its crash reports and its log in a temporary folder, never the user's.
         fieldcraft_io::recovery::use_automation_dir();
     }
+    let crashed = start_reporting();
     let options = eframe::NativeOptions {
         viewport: egui::ViewportBuilder::default()
             .with_title("FieldCraft")
@@ -177,12 +232,15 @@ fn main() -> eframe::Result {
         "FieldCraft",
         options,
         Box::new(move |cc| {
-            let mut app = ModelApp::new(Session::default()).with_services(services());
+            let mut session = Session::default();
+            // The window's model: its commands go into the crash journal.
+            session.crash_journal = crash::enabled();
+            let mut app = ModelApp::new(session).with_services(services());
             app.custom_titlebar = CUSTOM_TITLEBAR;
             app.integrated_titlebar = cfg!(target_os = "macos");
             if let Some(rs) = &cc.wgpu_render_state {
                 let info = rs.adapter.get_info();
-                eprintln!("fieldcraft: graphics {:?} {}, MSAA {}x (requested {MSAA}x)", info.backend, info.name, rs.msaa_samples);
+                log::info!("graphics {:?} {} ({}), MSAA {}x (requested {MSAA}x)", info.backend, info.name, info.driver, rs.msaa_samples);
                 app.set_wgpu(rs, DEPTH_BITS, rs.msaa_samples, &cc.egui_ctx);
             }
             if let Some(port) = args.control {
@@ -202,7 +260,8 @@ fn main() -> eframe::Result {
                 }
                 Autosaver::new(&dir).map_err(|e| log::warn!("autosave unavailable: {e}")).ok()
             });
-            Ok(Box::new(App { app, autosaver, autosaved_at: 0.0 }))
+            app.announce_crashes(&crashed);
+            Ok(Box::new(App { app, autosaver, autosaved_at: 0.0, running: false }))
         }),
     )
 }
diff --git a/crates/engine/src/bug_report.rs b/crates/engine/src/bug_report.rs
index 94c6048..3500e2f 100644
--- a/crates/engine/src/bug_report.rs
+++ b/crates/engine/src/bug_report.rs
@@ -255,6 +255,18 @@ pub fn draft(input: &Input, version: &str) -> Draft {
     Draft { title, fields, url, attachments, clipboard }
 }
 
+/// Write a draft's attachments to `bug-reports/<time>/` in the app's data folder (the user
+/// attaches them from there); returns the folder.
+pub fn save_attachments(draft: &Draft) -> Result<std::path::PathBuf, String> {
+    let root = fieldcraft_io::recovery::data_dir().ok_or("no data folder on this system")?;
+    let dir = root.join("bug-reports").join(crate::crash::stamp_now());
+    fieldcraft_io::fs::create_dir_all(&dir).map_err(|e| e.to_string())?;
+    for a in &draft.attachments {
+        fieldcraft_io::fs::write_atomic(&dir.join(&a.name), &a.bytes, false).map_err(|e| e.to_string())?;
+    }
+    Ok(dir)
+}
+
 /// The fields a link carries (for the review, when a field had to be cut).
 fn decode_fields(url: &str) -> Vec<(&'static str, String)> {
     let query = url.split_once('?').map_or("", |(_, q)| q);
diff --git a/crates/engine/src/cmd/file.rs b/crates/engine/src/cmd/file.rs
index 0558a49..a00a370 100644
--- a/crates/engine/src/cmd/file.rs
+++ b/crates/engine/src/cmd/file.rs
@@ -240,6 +240,7 @@ impl Session {
         opened.history = std::mem::take(&mut self.history);
         opened.limits = self.limits;
         opened.file_access = std::mem::take(&mut self.file_access);
+        opened.crash_journal = self.crash_journal;
         opened.clear_history();
         opened.mark_opened();
         *self = opened;
diff --git a/crates/ui-egui/src/appbar.rs b/crates/ui-egui/src/appbar.rs
index e027553..ac76023 100644
--- a/crates/ui-egui/src/appbar.rs
+++ b/crates/ui-egui/src/appbar.rs
@@ -336,7 +336,14 @@ fn help_menu(app: &mut ModelApp, ui: &mut egui::Ui) {
     ui.label("Left drag orbits (or pans or zooms: the navigation bar), right or middle drag pans, the wheel zooms, F or a double click fits.");
     ui.label(format!("S or {} searches every command; the command line at the bottom runs `id {{json}}`.", shortcut("K")));
     ui.separator();
+    let report = ui
+        .button("Report a Bug…")
+        .on_hover_text("Draft a GitHub issue with the version, the OS and the last error; nothing is sent until you submit it")
+        .clicked();
     ui.label(egui::RichText::new(format!("FieldCraft {}", crate::VERSION)).color(t.text_dim));
+    if report {
+        app.report_bug(None);
+    }
     if let Some(n) = open {
         app.ui.menu = None;
         app.open_sample(n);
diff --git a/crates/ui-egui/src/control.rs b/crates/ui-egui/src/control.rs
index e2c697d..8d8f2a5 100644
--- a/crates/ui-egui/src/control.rs
+++ b/crates/ui-egui/src/control.rs
@@ -164,6 +164,8 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
     let f = |k: &str| p.get(k).and_then(Value::as_f64).filter(|x| x.is_finite());
     let b = |k: &str| p.get(k).and_then(Value::as_bool).unwrap_or(false);
     let mods = || egui::Modifiers { shift: b("shift"), ctrl: b("ctrl"), command: b("ctrl"), alt: b("alt"), ..Default::default() };
+    // A crash nothing catches (#248) still says which request came last.
+    fieldcraft_engine::crash::activity(&format!("control {}", req.method));
     match req.method.as_str() {
         "engine.execute" => {
             let Some(id) = s("command") else { return err("missing `command`") };
@@ -202,6 +204,8 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
                 crate::files::Prompt::Design(p) => json!({"design": p}),
                 crate::files::Prompt::ReplaceMesh(r) => json!({"replace_mesh": r.question, "warnings": r.warnings}),
                 crate::files::Prompt::Delete(d) => json!({"delete": d.question(), "kind": d.kind, "name": d.name, "users": d.users, "allowed": d.allowed()}),
+                crate::files::Prompt::Crashed(r) => json!({"crashed": r}),
+                crate::files::Prompt::ReportBug => json!({"report_bug": app.report.as_ref().and_then(|f| f.drafted_json())}),
             }),
             "recent": app.recent.paths,
             "version": crate::VERSION,
@@ -374,6 +378,21 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
                     app.prompt = None;
                     ok(Value::Null)
                 }
+                (crate::files::Prompt::Crashed(r), Some("report")) => {
+                    app.report_bug(r.first().map(|c| c.id.clone()));
+                    ok(json!({"prompt": "report_bug"}))
+                }
+                (crate::files::Prompt::Crashed(_), Some("close" | "cancel")) => {
+                    app.prompt = None;
+                    ok(Value::Null)
+                }
+                // The form's fields; sending opens the browser, which only a click does.
+                (crate::files::Prompt::ReportBug, Some("set")) => wrap(app.set_report(p)),
+                (crate::files::Prompt::ReportBug, Some("close" | "cancel")) => {
+                    app.prompt = None;
+                    app.report = None;
+                    ok(Value::Null)
+                }
                 (crate::files::Prompt::Recover, Some("recover")) => match s("id") {
                     Some(id) => {
                         app.recover(id);
@@ -382,7 +401,7 @@ pub fn handle(app: &mut ModelApp, ctx: &egui::Context, req: &ControlRequest) ->
                     None => err("missing `id` (from file.recovery.list)"),
                 },
                 (_, a) => err(format!(
-                    "`answer` {a:?} does not answer this prompt (unsaved: save, discard, cancel; design: new, keep, cancel; replace_mesh: replace, cancel; delete: delete, cancel; recover: recover with id, close; samples: open with name, close)"
+                    "`answer` {a:?} does not answer this prompt (unsaved: save, discard, cancel; design: new, keep, cancel; replace_mesh: replace, cancel; delete: delete, cancel; recover: recover with id, close; samples: open with name, close; crashed: report, close; report_bug: set with title/observed/share_session/include_model, close)"
                 )),
             }
         }
diff --git a/crates/ui-egui/src/files.rs b/crates/ui-egui/src/files.rs
index 6bfb8e0..7c7a260 100644
--- a/crates/ui-egui/src/files.rs
+++ b/crates/ui-egui/src/files.rs
@@ -33,6 +33,8 @@ pub struct Filter {
 pub type PickOpen = Box<dyn Fn(&[Filter]) -> Option<String>>;
 /// The host picks where to save, starting from a file name; `None` when the user cancelled.
 pub type PickSave = Box<dyn Fn(&str, &[Filter]) -> Option<String>>;
+/// The host opens a web link in the user's browser.
+pub type OpenUrl = Box<dyn Fn(&str) -> Result<(), String>>;
 
 /// What the host provides: native file pickers and where the recent-files list is kept. The
 /// desktop app installs them; tests answer the pickers with closures.
@@ -44,6 +46,9 @@ pub struct Services {
     pub recent_path: Option<PathBuf>,
     /// The user's preferences file (JSON, [`Prefs`]); `None` keeps them for this run only.
     pub prefs_path: Option<PathBuf>,
+    /// Opens a link in the browser (Help › Report a Bug); without it, egui's own
+    /// `open_url` (the browser build opens the link itself).
+    pub open_url: Option<OpenUrl>,
 }
 
 const MODEL: Filter = Filter { name: "FieldCraft model", extensions: &["fieldcraft"] };
@@ -275,6 +280,10 @@ pub enum Prompt {
     /// Delete a definition (the item menu's Delete…, the Delete key): what uses it is listed, and
     /// the deletion refused or (a datum's partitions) done with it.
     Delete(crate::menu::DeleteAsk),
+    /// The last run crashed (its new crash reports, newest first): report it, or not now.
+    Crashed(Vec<fieldcraft_engine::crash::Summary>),
+    /// Help › Report a Bug ([`crate::report`]; the form is [`ModelApp::report`]).
+    ReportBug,
 }
 
 /// The answer to [`Prompt::Design`].
@@ -376,7 +385,14 @@ impl ModelApp {
         if self.ensure_idle().is_err() {
             return false;
         }
-        let base = if fresh { Session::default() } else { self.session.clone() };
+        // A fresh session is the app's own model too (its commands go into the crash journal).
+        let base = if fresh {
+            let mut s = Session::default();
+            s.crash_journal = self.session.crash_journal;
+            s
+        } else {
+            self.session.clone()
+        };
         let (rx, pending) = spawn(base, command, params);
         self.set_status(format!("{title}…"), false);
         self.loading = Some(Loading { title, done, recent, form: None, rx, pending, shown: false });
@@ -730,6 +746,7 @@ impl ModelApp {
             }
             "file.recover" | "file.recovery.list" => self.prompt = Some(Prompt::Recover),
             "file.sample" => self.prompt = Some(Prompt::Samples),
+            "diagnostics.bug_report" | "diagnostics.crash_reports" | "diagnostics.crash_report" => self.report_bug(None),
             "solve.run" => self.solve_all(),
             "deck.write" if can_save => match preset.get("format").and_then(Value::as_str) {
                 Some(f) => self.write_deck(f),
@@ -989,7 +1006,8 @@ pub fn show(app: &mut ModelApp, ctx: &egui::Context) {
                 app.prompt = None;
             }
         }
-        None => {}
+        // Drawn by `crate::report::show`.
+        Some(Prompt::Crashed(_) | Prompt::ReportBug) | None => {}
     }
 }
 
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 0c61c1a..58033a7 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -40,6 +40,7 @@ pub mod menu;
 pub mod navigation;
 pub mod palette;
 pub mod reply;
+pub mod report;
 pub mod results;
 pub mod results_panel;
 pub mod samples;
@@ -390,6 +391,10 @@ pub struct ModelApp {
     pub queued: std::collections::VecDeque<String>,
     /// The question the window is asking (unsaved changes, recover).
     pub prompt: Option<files::Prompt>,
+    /// Help › Report a Bug's form, while open ([`files::Prompt::ReportBug`]).
+    pub report: Option<report::ReportForm>,
+    /// The last error the status bar showed (what Report a Bug starts from).
+    pub last_error: Option<String>,
     /// A design opened over a model of another part, waiting for [`files::Prompt::Design`]'s answer.
     pub held: Option<files::Opened>,
     /// The window draws its own title bar and caption buttons (Windows, Linux).
@@ -468,6 +473,8 @@ impl ModelApp {
             loading: None,
             queued: std::collections::VecDeque::new(),
             prompt: None,
+            report: None,
+            last_error: None,
             held: None,
             custom_titlebar: false,
             integrated_titlebar: false,
@@ -783,6 +790,7 @@ impl ModelApp {
         let text = text.into();
         if error {
             log::warn!("{text}");
+            self.last_error = Some(text.clone());
         }
         self.status = Some(Status { text, error });
     }
@@ -1442,6 +1450,7 @@ impl ModelApp {
         egui::CentralPanel::default().frame(egui::Frame::NONE).show(ui, |ui| viewport::show(self, ui));
         palette::popup(self, ui.ctx());
         files::show(self, ui.ctx());
+        report::show(self, ui.ctx());
         if self.custom_titlebar {
             titlebar::resize_zones(ui);
         }
diff --git a/crates/ui-egui/src/report.rs b/crates/ui-egui/src/report.rs
new file mode 100644
index 0000000..d591bf1
--- /dev/null
+++ b/crates/ui-egui/src/report.rs
@@ -0,0 +1,368 @@
+//! Help › Report a Bug, and the question the window asks after a crash ("FieldCraft closed
+//! unexpectedly — Report it").
+//!
+//! The form shows exactly what the GitHub issue form will be filled with
+//! ([`fieldcraft_engine::bug_report`]): the version, the OS, what happened (the last error by
+//! default) and, after a crash, where it happened. **Share my session** adds the commands that
+//! built the model, **Include the model file** the model as well. Nothing leaves the computer
+//! until the user clicks **Open GitHub Issue**, which opens the filled form in their browser (they
+//! submit it there, or not); files too big for the link are saved to a folder to attach from, and
+//! a long session is also put on the clipboard.
+
+use egui::RichText;
+use fieldcraft_engine::bug_report::{self, Draft, Input};
+use fieldcraft_engine::crash::{self, Summary};
+use serde_json::{Value, json};
+
+use crate::ModelApp;
+use crate::files::Prompt;
+
+/// The Report a Bug form.
+#[derive(Debug, Default)]
+pub struct ReportForm {
+    pub title: String,
+    pub observed: String,
+    /// The crash report being reported (its id).
+    pub crash: Option<String>,
+    pub share_session: bool,
+    pub include_model: bool,
+    /// What the draft is built from (the session's commands and model, or the crash report's),
+    /// read when the form opens and when the model is first included.
+    input: Input,
+    model_read: bool,
+    /// The draft, and the form state it was made for.
+    draft: Option<Draft>,
+    drafted: Option<Key>,
+    /// Why the input could not be read.
+    pub problem: Option<String>,
+}
+
+type Key = (String, String, bool, bool);
+
+impl ReportForm {
+    /// The form and its draft as last made (for `ui.inspect`).
+    pub fn drafted_json(&self) -> Option<Value> {
+        let mut v = self.draft.as_ref()?.to_json();
+        v["share_session"] = json!(self.share_session);
+        v["include_model"] = json!(self.include_model);
+        v["crash"] = json!(self.crash);
+        Some(v)
+    }
+
+    /// The draft for the form as it is now (made again only when something changed).
+    pub fn draft(&mut self) -> &Draft {
+        let key = (self.title.clone(), self.observed.clone(), self.share_session, self.include_model);
+        if self.drafted.as_ref() != Some(&key) {
+            self.draft = None;
+            self.drafted = Some(key);
+        }
+        self.draft.get_or_insert_with(|| {
+            let mut input = self.input.clone();
+            input.title = self.title.clone();
+            input.observed = self.observed.clone();
+            input.share_session = self.share_session;
+            input.include_model = self.include_model;
+            bug_report::draft(&input, &crash::Build::current().version_line())
+        })
+    }
+}
+
+/// The input for `form` from the session (or its crash report).
+fn read_input(app: &ModelApp, form: &ReportForm) -> Result<Input, String> {
+    let mut p = json!({"share_session": true, "include_model": form.include_model});
+    if let Some(id) = &form.crash {
+        p["crash"] = json!(id);
+    }
+    fieldcraft_engine::cmd::diagnostics::bug_report_input(&app.session, &p).map_err(|e| e.to_string())
+}
+
+impl ModelApp {
+    /// Open Help › Report a Bug, for `crash` (a report's id) or what happened last.
+    pub fn report_bug(&mut self, crash: Option<String>) {
+        let mut form = ReportForm {
+            observed: if crash.is_some() { String::new() } else { self.last_error.clone().unwrap_or_default() },
+            crash,
+            ..Default::default()
+        };
+        match read_input(self, &form) {
+            Ok(input) => form.input = input,
+            Err(e) => form.problem = Some(e),
+        }
+        self.report = Some(form);
+        self.prompt = Some(Prompt::ReportBug);
+        self.ui.menu = None;
+    }
+
+    /// The host found these crash reports at startup: ask about the real crashes.
+    pub fn announce_crashes(&mut self, fresh: &[Summary]) {
+        let crashes: Vec<Summary> = fresh.iter().filter(|r| r.kind != "recovered_panic").cloned().collect();
+        if crashes.is_empty() {
+            return;
+        }
+        log::warn!(
+            "{} crash report(s) since the last start: {}",
+            crashes.len(),
+            crashes.iter().map(|c| c.id.as_str()).collect::<Vec<_>>().join(", ")
+        );
+        if self.prompt.is_none() {
+            self.prompt = Some(Prompt::Crashed(crashes));
+        }
+    }
+
+    /// Change the open form (`ui.prompt` `set`): any of title, observed, share_session,
+    /// include_model.
+    pub fn set_report(&mut self, p: &Value) -> Result<Value, String> {
+        let mut form = self.report.take().ok_or("Report a Bug is not open")?;
+        if let Some(t) = p.get("title").and_then(Value::as_str) {
+            form.title = t.chars().take(500).collect();
+        }
+        if let Some(t) = p.get("observed").and_then(Value::as_str) {
+            form.observed = t.chars().take(20_000).collect();
+        }
+        if let Some(b) = p.get("share_session").and_then(Value::as_bool) {
+            form.share_session = b;
+        }
+        if let Some(b) = p.get("include_model").and_then(Value::as_bool) {
+            form.include_model = b;
+        }
+        self.include_model_if_asked(&mut form);
+        let draft = form.draft().to_json();
+        self.report = Some(form);
+        Ok(draft)
+    }
+
+    /// Read the model once it is first included.
+    fn include_model_if_asked(&mut self, form: &mut ReportForm) {
+        if form.include_model && !form.model_read {
+            form.model_read = true;
+            match read_input(self, form) {
+                Ok(input) => form.input = input,
+                Err(e) => form.problem = Some(e),
+            }
+        }
+    }
+
+    /// Open the draft in the browser: attachments saved to a folder of their own, the session on
+    /// the clipboard when it is too long for the link.
+    fn send_report(&mut self, ctx: &egui::Context, draft: &Draft) {
+        let mut saved = None;
+        if !draft.attachments.is_empty() {
+            match bug_report::save_attachments(draft) {
+                Ok(dir) => saved = Some(dir),
+                Err(e) => {
+                    self.set_status(format!("Report a Bug: could not save the files to attach: {e}"), true);
+                    return;
+                }
+            }
+        }
+        if let Some(text) = &draft.clipboard {
+            ctx.copy_text(text.clone());
+        }
+        match &self.services.open_url {
+            Some(open) => {
+                if let Err(e) = open(&draft.url) {
+                    self.set_status(format!("Report a Bug: could not open the browser: {e}"), true);
+                    return;
+                }
+            }
+            None => ctx.open_url(egui::OpenUrl::new_tab(draft.url.clone())),
+        }
+        log::info!("bug report opened in the browser ({} bytes, {} attachment(s))", draft.url.len(), draft.attachments.len());
+        let text = match saved {
+            Some(dir) => format!("The issue form opened in your browser: attach the files in {} and submit it there.", dir.display()),
+            None => "The issue form opened in your browser: review it and submit it there.".to_string(),
+        };
+        self.set_status(text, false);
+        self.prompt = None;
+        self.report = None;
+    }
+}
+
+fn size(bytes: usize) -> String {
+    if bytes < 1024 { format!("{bytes} B") } else { format!("{} KB", bytes.div_ceil(1024)) }
+}
+
+fn kind_label(kind: &str) -> &'static str {
+    match kind {
+        "unclean_exit" => "FieldCraft closed unexpectedly",
+        "command_panic" => "A command hit an internal error",
+        _ => "FieldCraft hit an internal error",
+    }
+}
+
+/// The crash question and the Report a Bug form, when open.
+pub fn show(app: &mut ModelApp, ctx: &egui::Context) {
+    let t = crate::theme::Tokens::get(app.ui.dark);
+    match app.prompt.clone() {
+        Some(Prompt::Crashed(reports)) => {
+            let Some(first) = reports.first() else {
+                app.prompt = None;
+                return;
+            };
+            let (mut report, mut close) = (false, false);
+            crate::frame::window(ctx, kind_label(&first.kind), crate::frame::Width::Normal).id(egui::Id::new("fc_crashed")).show(ctx, |ui| {
+                ui.label(match first.kind.as_str() {
+                    "unclean_exit" => "FieldCraft closed unexpectedly the last time it ran.",
+                    _ => "FieldCraft hit an internal error the last time it ran.",
+                });
+                ui.label(RichText::new(&first.message).color(t.text_dim));
+                if reports.len() > 1 {
+                    ui.label(RichText::new(format!("And {} more since.", reports.len() - 1)).color(t.text_dim));
+                }
+                ui.add_space(4.0);
+                ui.label(
+                    RichText::new(
+                        "A crash report was saved on this computer. Reporting it opens a GitHub issue you review first; nothing is sent until you submit it.",
+                    )
+                    .color(t.text_dim),
+                );
+                ui.add_space(6.0);
+                ui.horizontal(|ui| {
+                    report = ui.button("Report It…").clicked();
+                    close = ui.button("Not Now").clicked();
+                });
+            });
+            if report {
+                app.report_bug(Some(first.id.clone()));
+            } else if close || ctx.input(|i| i.key_pressed(egui::Key::Escape)) {
+                app.prompt = None;
+            }
+        }
+        Some(Prompt::ReportBug) => {
+            let Some(mut form) = app.report.take() else {
+                app.prompt = None;
+                return;
+            };
+            let (mut send, mut close) = (false, false);
+            let commands = form.input.commands.len();
+            crate::frame::window(ctx, "Report a Bug", crate::frame::Width::Wide).id(egui::Id::new("fc_report_bug")).show(ctx, |ui| {
+                ui.label(
+                    RichText::new(
+                        "This opens a GitHub issue in your browser, filled in with what is shown below. Nothing is sent until you submit it there.",
+                    )
+                    .color(t.text_dim),
+                );
+                if let Some(p) = &form.problem {
+                    ui.label(RichText::new(p).color(t.error));
+                }
+                ui.add_space(4.0);
+                ui.label("Title");
+                let hint = form.draft().title.clone();
+                ui.add(egui::TextEdit::singleline(&mut form.title).hint_text(hint).desired_width(f32::INFINITY));
+                ui.label("What happened");
+                ui.add(
+                    egui::TextEdit::multiline(&mut form.observed)
+                        .hint_text("What you did, and what went wrong")
+                        .desired_rows(3)
+                        .desired_width(f32::INFINITY),
+                );
+                ui.add_space(4.0);
+                ui.checkbox(&mut form.share_session, "Share my session")
+                    .on_hover_text("Attach the commands that built the model, to replay it. They can name your files.");
+                ui.label(
+                    RichText::new(format!("The {commands} command(s) that built the model, the version and the OS; they can name your files."))
+                        .color(t.text_dim)
+                        .size(11.0),
+                );
+                ui.add_enabled_ui(form.share_session, |ui| {
+                    ui.checkbox(&mut form.include_model, "Include the model file")
+                        .on_hover_text("Attach the model too (you attach the file yourself).");
+                });
+                if !form.share_session {
+                    form.include_model = false;
+                }
+                app.include_model_if_asked(&mut form);
+                let draft = form.draft().clone();
+                ui.add_space(6.0);
+                ui.horizontal(|ui| {
+                    send = ui.button("Open GitHub Issue").clicked();
+                    close = ui.button("Cancel").clicked();
+                });
+                ui.add_space(4.0);
+                egui::CollapsingHeader::new("What is sent").id_salt("fc_report_sent").default_open(true).show(ui, |ui| {
+                    egui::ScrollArea::vertical().max_height(180.0).show(ui, |ui| {
+                        ui.label(RichText::new(format!("Title: {}", draft.title)).monospace().size(11.0));
+                        for (k, v) in &draft.fields {
+                            if !v.is_empty() {
+                                ui.label(RichText::new(format!("{k}:")).strong().size(11.0));
+                                ui.label(RichText::new(v).monospace().size(11.0));
+                            }
+                        }
+                        for a in &draft.attachments {
+                            ui.label(RichText::new(format!("Attach {} ({}): {}", a.name, size(a.bytes.len()), a.what)).size(11.0).color(t.accent));
+                        }
+                        if draft.clipboard.is_some() {
+                            ui.label(RichText::new("The session goes on the clipboard too, to paste.").size(11.0).color(t.text_dim));
+                        }
+                    });
+                });
+            });
+            let draft = form.draft().clone();
+            app.report = Some(form);
+            if send {
+                app.send_report(ctx, &draft);
+            } else if close || ctx.input(|i| i.key_pressed(egui::Key::Escape)) {
+                app.prompt = None;
+                app.report = None;
+            }
+        }
+        _ => {}
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use fieldcraft_engine::Session;
+
+    #[test]
+    fn report_a_bug_shows_the_last_error_and_shares_only_when_ticked() {
+        let mut app = ModelApp::new(Session::default());
+        app.run("mesh.node.add", json!({"label": 1, "xyz": [0, 0, 0]})).unwrap();
+        let _ = app.run("mesh.node.remove", json!({"label": 99}));
+        let error = app.last_error.clone().expect("the failure is the last error");
+        app.report_bug(None);
+        assert_eq!(app.prompt, Some(Prompt::ReportBug));
+        let form = app.report.as_mut().unwrap();
+        assert_eq!(form.observed, error);
+        let d = form.draft().clone();
+        assert!(d.attachments.is_empty() && !bug_report_text(&d).contains("mesh.node.add"), "no session unless shared");
+        let d = app.set_report(&json!({"share_session": true})).unwrap();
+        assert!(d["url"].as_str().unwrap().contains("mesh.node.add"), "{d}");
+        let d = app.set_report(&json!({"include_model": true})).unwrap();
+        assert_eq!(d["attachments"][0]["name"], "model.fieldcraft", "{d}");
+        // The model goes only with the session.
+        let d = app.set_report(&json!({"share_session": false})).unwrap();
+        assert_eq!(d["attachments"], json!([]), "{d}");
+    }
+
+    fn bug_report_text(d: &Draft) -> String {
+        d.fields.iter().map(|(_, v)| v.as_str()).collect::<Vec<_>>().join("\n")
+    }
+
+    #[test]
+    fn a_crash_at_startup_asks_and_report_it_opens_the_form() {
+        let mut app = ModelApp::new(Session::default());
+        let quiet = Summary {
+            id: "20261014-101500-0000000000000001".into(),
+            kind: "recovered_panic".into(),
+            time: String::new(),
+            message: String::new(),
+            command: None,
+            count: 1,
+            version: String::new(),
+            path: String::new(),
+            replayable: false,
+        };
+        app.announce_crashes(std::slice::from_ref(&quiet));
+        assert_eq!(app.prompt, None, "recovered panics do not interrupt");
+        let crashed = Summary { kind: "unclean_exit".into(), message: "FieldCraft ended without a clean exit".into(), ..quiet };
+        app.announce_crashes(std::slice::from_ref(&crashed));
+        assert!(matches!(&app.prompt, Some(Prompt::Crashed(r)) if r.len() == 1));
+        app.report_bug(Some(crashed.id.clone()));
+        let form = app.report.as_ref().unwrap();
+        assert_eq!(form.crash.as_deref(), Some(crashed.id.as_str()));
+        // The report is not in this test's crash folder: the form says so and still drafts.
+        assert!(form.problem.as_deref().is_some_and(|p| p.contains("no crash report")), "{:?}", form.problem);
+    }
+}