diff --git a/ROADMAP.md b/ROADMAP.md
index 8c1d8367..962bd5e7 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -131,6 +131,7 @@ app's JSON control channel (`deckcraft --control PORT`).
 
 | Date | What landed |
 |---|---|
+| 2026-10-17 | Opening a file caps absurd effect sizes (glow, soft edges, shadows, reflections, on shapes, text and table text) at what Format Shape allows: a glow of 10^18 pt in a .pptx made rendering ask for 34 GB and abort |
 | 2026-10-15 | PPTX trigger sequences keep separate On Click steps, including paragraph builds; synthetic import/edit/save/reopen and headless show regressions |
 | 2026-10-15 | CLI: .txt and .md export includes table cell text, which it used to skip silently (#814) |
 | 2026-10-15 | A `.pptx` slide that can't be read is reported, not dropped in silence: `lostSlides` from `file.open`, a message and a repaired copy in the app, a warning from `deckcraft-cli` (#203) |
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 9e5c6e55..b9185556 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -3677,3 +3677,105 @@ fn opening_a_pptx_with_an_unreadable_slide_says_so() {
     assert_eq!(r["lostSlides"], json!([]), "{r}");
     assert!(u.ui_requests.is_empty());
 }
+
+/// A file with absurd effect sizes opens with them capped at what Format Shape allows: drawn as
+/// they were, a glow of 10^18 pt made the renderer ask for 34 GB and abort.
+#[test]
+fn opening_a_file_caps_absurd_effect_sizes() {
+    use deckcraft_model::style::{Glow, Reflection};
+    let mut s = Session::with_new();
+    s.execute("slide.new", &json!({"layout": "blank"})).unwrap();
+    s.execute("shape.insert", &json!({"preset": "rect", "rect": [100, 100, 200, 100], "text": "Glow"})).unwrap();
+    s.execute("shape.effects", &json!({"shadow": "outer", "reflection": "tight", "softEdges": 4, "glow": {"radius": 8}})).unwrap();
+    s.execute("insert.table", &json!({"rows": 1, "cols": 1, "rect": [400, 300, 100, 40]})).unwrap();
+    let huge = 1e18;
+    s.edit(|doc, sel| {
+        let list = crate::shapes_mut(doc, sel).unwrap();
+        for sh in list.iter_mut() {
+            if let Some(e) = sh.effects.as_mut() {
+                e.glow.as_mut().unwrap().radius = huge;
+                e.soft_edge = Some(f64::NAN);
+                let sw = e.outer_shadow.as_mut().unwrap();
+                (sw.blur, sw.dist, sw.sx) = (huge, huge, huge);
+                *e.reflection.as_mut().unwrap() = Reflection { blur: huge, start_alpha: 0.5, end_alpha: 0.0, end_pos: 0.5, dist: huge };
+            }
+            let glow = Some(Glow { color: deckcraft_model::style::ColorRef::rgb(deckcraft_color::Rgba::BLACK), radius: huge });
+            let runs: Vec<&mut deckcraft_model::text::Run> = match &mut sh.kind {
+                deckcraft_model::ShapeKind::Table(t) => t
+                    .rows
+                    .iter_mut()
+                    .flat_map(|r| r.cells.iter_mut())
+                    .flat_map(|c| c.text.paragraphs.iter_mut())
+                    .flat_map(|p| p.runs.iter_mut())
+                    .collect(),
+                _ => sh.text.iter_mut().flat_map(|t| t.paragraphs.iter_mut()).flat_map(|p| p.runs.iter_mut()).collect(),
+            };
+            for r in runs {
+                r.props.glow = glow.clone();
+            }
+        }
+        // Inherited styles too: the deck default, a master's body style, a text box's own list
+        // style, and the theme's effect styles that shape styles point at.
+        let level = deckcraft_model::text::LevelStyle {
+            run: deckcraft_model::text::RunProps {
+                glow: Some(Glow { color: deckcraft_model::style::ColorRef::rgb(deckcraft_color::Rgba::BLACK), radius: huge }),
+                ..Default::default()
+            },
+            ..Default::default()
+        };
+        doc.default_text_style.set(0, level.clone());
+        let m = std::sync::Arc::make_mut(&mut doc.masters[0]);
+        m.body_style.set(0, level.clone());
+        if let Some(fx) = m.theme.format.effects.first_mut() {
+            fx.glow = Some(Glow { color: deckcraft_model::style::ColorRef::rgb(deckcraft_color::Rgba::BLACK), radius: huge });
+        }
+        let list = crate::shapes_mut(doc, sel).unwrap();
+        if let Some(t) = list.iter_mut().find_map(|sh| sh.text.as_mut()) {
+            t.list_style.set(0, level);
+        }
+        Ok(())
+    })
+    .unwrap();
+    for format in ["deckcraft", "pptx"] {
+        let bytes = cmd::file::save_bytes(&s.doc().unwrap().doc, format).unwrap();
+        let mut t = Session::new();
+        t.execute("file.openBytes", &json!({"name": format!("fx.{format}"), "data": cmd::base64_encode(&bytes)})).unwrap();
+        let st = t.doc().unwrap();
+        let slide = st.doc.slides.last().unwrap();
+        let mut glows = vec![];
+        deckcraft_model::walk(&slide.shapes, &mut |sh, _| {
+            if let Some(e) = &sh.effects {
+                glows.extend(e.glow.as_ref().map(|g| g.radius));
+                assert!(e.soft_edge.is_none_or(|v| (0.0..=100.0).contains(&v)), "{format}: {:?}", e.soft_edge);
+                if let Some(sw) = &e.outer_shadow {
+                    assert!(sw.blur <= 200.0 && sw.dist <= 200.0 && sw.sx <= 10.0, "{format}: {sw:?}");
+                }
+                if let Some(r) = &e.reflection {
+                    assert!(r.blur <= 100.0 && r.dist <= 100.0, "{format}: {r:?}");
+                }
+            }
+            for p in sh.text.iter().flat_map(|t| t.paragraphs.iter()) {
+                glows.extend(p.runs.iter().filter_map(|r| r.props.glow.as_ref().map(|g| g.radius)));
+            }
+            if let deckcraft_model::ShapeKind::Table(tb) = &sh.kind {
+                let cells = tb.rows.iter().flat_map(|r| r.cells.iter()).flat_map(|c| c.text.paragraphs.iter());
+                glows.extend(cells.flat_map(|p| p.runs.iter()).filter_map(|r| r.props.glow.as_ref().map(|g| g.radius)));
+            }
+        });
+        let inherited = |ls: &deckcraft_model::text::ListStyle| {
+            ls.levels.iter().flatten().filter_map(|l| l.run.glow.as_ref().map(|g| g.radius)).collect::<Vec<_>>()
+        };
+        glows.extend(inherited(&st.doc.default_text_style));
+        let m = &st.doc.masters[0];
+        for ls in [&m.title_style, &m.body_style, &m.other_style] {
+            glows.extend(inherited(ls));
+        }
+        glows.extend(m.theme.format.effects.iter().filter_map(|e| e.glow.as_ref().map(|g| g.radius)));
+        deckcraft_model::walk(&slide.shapes, &mut |sh, _| glows.extend(sh.text.iter().flat_map(|t| inherited(&t.list_style))));
+        assert!(!glows.is_empty(), "{format}: the glows were kept");
+        assert!(glows.iter().all(|g| (0.0..=150.0).contains(g)), "{format}: {glows:?}");
+        // Capped, the slide renders (checked last: uncapped, this is what ran out of memory).
+        let i = st.doc.slides.len() - 1;
+        t.execute("file.render", &json!({"slide": i, "scale": 0.1})).unwrap();
+    }
+}
diff --git a/crates/format/src/lib.rs b/crates/format/src/lib.rs
index c2837a20..f987a2b7 100644
--- a/crates/format/src/lib.rs
+++ b/crates/format/src/lib.rs
@@ -350,6 +350,66 @@ fn sane_xfrm(x: &mut deckcraft_model::Xfrm) {
 
 fn sane_run(p: &mut deckcraft_model::text::RunProps) {
     p.size = p.size.filter(|v| v.is_finite() && *v > 0.0).map(|v| v.clamp(1.0, 4000.0));
+    for s in p.shadow.iter_mut().chain(p.inner_shadow.iter_mut()) {
+        sane_shadow(s);
+    }
+    if let Some(g) = p.glow.as_mut() {
+        g.radius = effect_size(g.radius, MAX_GLOW);
+    }
+    if let Some(r) = p.reflection.as_mut() {
+        sane_reflection(r);
+    }
+    p.soft_edge = p.soft_edge.map(|v| effect_size(v, MAX_SOFT_EDGE));
+}
+
+/// The largest effect sizes, in points: what Format Shape and `shape.effects` allow. A file can
+/// say anything, and the renderer's memory grows with these (a glow of 10^18 pt asked for 34 GB).
+const MAX_GLOW: f64 = 150.0;
+const MAX_SOFT_EDGE: f64 = 100.0;
+const MAX_SHADOW: f64 = 200.0;
+const MAX_REFLECTION: f64 = 100.0;
+
+/// `v` within 0..=`max`; not a number is 0.
+fn effect_size(v: f64, max: f64) -> f64 {
+    if v.is_finite() { v.clamp(0.0, max) } else { 0.0 }
+}
+
+fn sane_shadow(s: &mut deckcraft_model::style::Shadow) {
+    s.blur = effect_size(s.blur, MAX_SHADOW);
+    s.dist = effect_size(s.dist, MAX_SHADOW);
+    s.dir = if s.dir.is_finite() { s.dir.rem_euclid(360.0) } else { 0.0 };
+    // Perspective scale (1 = 100%) and skew (degrees).
+    for v in [&mut s.sx, &mut s.sy] {
+        *v = if v.is_finite() { v.clamp(-10.0, 10.0) } else { 1.0 };
+    }
+    for v in [&mut s.kx, &mut s.ky] {
+        *v = if v.is_finite() { v.clamp(-89.0, 89.0) } else { 0.0 };
+    }
+}
+
+fn sane_reflection(r: &mut deckcraft_model::style::Reflection) {
+    r.blur = effect_size(r.blur, MAX_REFLECTION);
+    r.dist = effect_size(r.dist, MAX_REFLECTION);
+}
+
+/// Run properties a list style hands down to the text that inherits it.
+fn sane_list_style(ls: &mut deckcraft_model::text::ListStyle) {
+    for level in ls.levels.iter_mut().flatten() {
+        sane_run(&mut level.run);
+    }
+}
+
+fn sane_effects(e: &mut deckcraft_model::Effects) {
+    for s in e.outer_shadow.iter_mut().chain(e.inner_shadow.iter_mut()) {
+        sane_shadow(s);
+    }
+    if let Some(g) = e.glow.as_mut() {
+        g.radius = effect_size(g.radius, MAX_GLOW);
+    }
+    e.soft_edge = e.soft_edge.map(|v| effect_size(v, MAX_SOFT_EDGE));
+    if let Some(r) = e.reflection.as_mut() {
+        sane_reflection(r);
+    }
 }
 
 fn sane_shapes(shapes: &mut [deckcraft_model::Shape], depth: usize) {
@@ -363,7 +423,11 @@ fn sane_shapes(shapes: &mut [deckcraft_model::Shape], depth: usize) {
         if let Some(l) = sh.line.as_mut() {
             l.width = l.width.filter(|v| v.is_finite() && *v >= 0.0).map(|v| v.min(1584.0));
         }
+        if let Some(e) = sh.effects.as_mut() {
+            sane_effects(e);
+        }
         if let Some(t) = sh.text.as_mut() {
+            sane_list_style(&mut t.list_style);
             for para in &mut t.paragraphs {
                 sane_run(&mut para.end_props);
                 for r in &mut para.runs {
@@ -381,6 +445,17 @@ fn sane_shapes(shapes: &mut [deckcraft_model::Shape], depth: usize) {
                 sane_xfrm(child);
                 sane_shapes(children, depth + 1);
             }
+            deckcraft_model::ShapeKind::Table(t) => {
+                for cell in t.rows.iter_mut().flat_map(|r| r.cells.iter_mut()) {
+                    sane_list_style(&mut cell.text.list_style);
+                }
+                for para in t.rows.iter_mut().flat_map(|r| r.cells.iter_mut()).flat_map(|c| c.text.paragraphs.iter_mut()) {
+                    sane_run(&mut para.end_props);
+                    for r in &mut para.runs {
+                        sane_run(&mut r.props);
+                    }
+                }
+            }
             _ => {}
         }
     }
@@ -395,12 +470,21 @@ pub fn sane_numbers(p: &mut Presentation) {
             *slide = Arc::new(fixed);
         }
     }
+    // What text and shapes inherit: the deck's default text style, each master's title, body and
+    // other styles, and the theme's effect styles that shape styles point at.
+    sane_list_style(&mut p.default_text_style);
     for m in p.masters.iter_mut().chain(p.notes_master.iter_mut()).chain(p.handout_master.iter_mut()) {
         let mut fixed = (**m).clone();
         sane_shapes(&mut fixed.shapes, 0);
         for l in &mut fixed.layouts {
             sane_shapes(&mut l.shapes, 0);
         }
+        for ls in [&mut fixed.title_style, &mut fixed.body_style, &mut fixed.other_style] {
+            sane_list_style(ls);
+        }
+        for e in &mut fixed.theme.format.effects {
+            sane_effects(e);
+        }
         if fixed != **m {
             *m = Arc::new(fixed);
         }