diff --git a/crates/rustmotion-html/src/element.rs b/crates/rustmotion-html/src/element.rs
index c308265a..b370f658 100644
--- a/crates/rustmotion-html/src/element.rs
+++ b/crates/rustmotion-html/src/element.rs
@@ -2,7 +2,9 @@ use markup5ever_rcdom::{Handle, NodeData};
 use serde_json::{Map, Value};
 
 use crate::style::{coerce_value, parse_anim_attr, parse_inline_style};
-use crate::{element_attrs, tag_name, HtmlError};
+use crate::{check_known_attrs, element_attrs, tag_name, HtmlError};
+
+const KNOWN_NATIVE_ATTRS: &[&str] = &["style", "anim"];
 
 enum TagKind {
     Container,
@@ -90,6 +92,7 @@ pub(crate) fn element_to_value(handle: &Handle) -> Result<Option<Value>, HtmlErr
             suggestion: suggestion.to_string(),
         }),
         TagKind::Text => {
+            check_known_attrs(&tag, &attrs, KNOWN_NATIVE_ATTRS)?;
             let mut obj = Map::new();
             obj.insert("type".into(), Value::from("text"));
             obj.insert("content".into(), Value::from(inner_text(handle)));
@@ -99,6 +102,7 @@ pub(crate) fn element_to_value(handle: &Handle) -> Result<Option<Value>, HtmlErr
             Ok(Some(Value::Object(obj)))
         }
         TagKind::Container => {
+            check_known_attrs(&tag, &attrs, KNOWN_NATIVE_ATTRS)?;
             let mut obj = Map::new();
             obj.insert("type".into(), Value::from("div"));
             if let Some(style) = style_object(&attrs)? {
diff --git a/crates/rustmotion-html/src/lib.rs b/crates/rustmotion-html/src/lib.rs
index 092bd1d8..69d9ea43 100644
--- a/crates/rustmotion-html/src/lib.rs
+++ b/crates/rustmotion-html/src/lib.rs
@@ -97,6 +97,44 @@ pub enum HtmlError {
         "<scene> found nested inside <{parent}> — <scene> elements must be direct children of <rustmotion> (only <font> is recursed into)"
     )]
     NestedScene { parent: String },
+    /// Emitted when an element carries an attribute the transpiler never
+    /// reads. `<rustmotion>`, `<scene>`, and native container/text tags only
+    /// ever consume a fixed, small set of attribute names — anything else
+    /// used to vanish with no trace, invisible to `--strict-attrs` because
+    /// it never reached the emitted JSON in the first place.
+    #[error("<{element}> has unsupported attribute(s): {detail} — these are silently ignored today; fix the typo, drop them, or use the attribute the dialect actually reads")]
+    UnknownAttributes { element: String, detail: String },
+    /// Emitted for a `<scene>`'s `world-position` attribute that is neither
+    /// `"x,y"` nor a JSON `{"x":..,"y":..}` object.
+    #[error("world-position=\"{0}\" is not \"x,y\" or a JSON object {{\"x\":..,\"y\":..}}")]
+    InvalidWorldPosition(String),
+    /// Emitted for a `<scene>`'s `animated-background` attribute when its
+    /// value starts with `{`/`[` but fails to parse as JSON.
+    #[error("animated-background attribute contains invalid JSON: {0}")]
+    InvalidAnimatedBackgroundJson(String),
+    /// Emitted for a `style="..."` declaration whose value has more than one
+    /// top-level (paren-aware) token and isn't one of the shorthands the
+    /// transpiler knows how to expand (`padding`/`margin`/`border-radius`'s
+    /// 1-4 value box form, `grid-template-columns`/`-rows`'s track list with
+    /// `repeat()`/`minmax()`). Every other multi-token value used to become
+    /// an opaque string the core length parser cannot read, silently
+    /// resolving to `0px`.
+    #[error("style property '{prop}' has an unsupported multi-token value '{value}' — supported multi-token forms are the padding/margin/border-radius box shorthand and grid-template-columns/-rows track lists with repeat()/minmax(); rewrite as a single value")]
+    UnsupportedStyleShorthand { prop: String, value: String },
+    /// Emitted when a `<script>`/`<img>`/`<svg>`/`<rm-*>`/container element
+    /// is found nested inside an inline text element (`p`/`span`/`h1..h6`/
+    /// `strong`/`em`/`label`). Those flatten their whole subtree to a plain
+    /// string — a nested element with real content (a component, a shape, a
+    /// child container) has nowhere to go and used to either bleed its raw
+    /// source into the string or vanish outright.
+    #[error("<{tag}> cannot appear inside an inline text element (p/span/h1..h6/strong/em/label) — those flatten their content to a plain string, so <{tag}>'s own content would be silently lost; move it outside as a sibling, or wrap the text in a <div>/<rm-*> container instead")]
+    TextContentUnsupportedChild { tag: String },
+    /// Emitted when the HTML serializer itself fails (I/O error into an
+    /// in-memory buffer, or non-UTF-8 output) inside the studio write-back
+    /// path. The write-back functions refuse (return `None`) rather than
+    /// hand the caller a partial or empty buffer to write to disk.
+    #[error("failed to serialize the rewritten HTML: {0}")]
+    SerializeFailed(String),
 }
 
 /// Transpile an HTML-dialect document into the scenario `serde_json::Value` that
@@ -108,6 +146,12 @@ pub fn html_to_scenario_value(html: &str) -> Result<Value, HtmlError> {
     let attrs = element_attrs(&root);
     let get = |k: &str| attrs.iter().find(|(n, _)| n == k).map(|(_, v)| v.clone());
 
+    check_known_attrs(
+        "rustmotion",
+        &attrs,
+        &["width", "height", "fps", "background", "codec", "crf"],
+    )?;
+
     let width = get("width").ok_or(HtmlError::MissingDimensions)?;
     let height = get("height").ok_or(HtmlError::MissingDimensions)?;
 
@@ -120,6 +164,12 @@ pub fn html_to_scenario_value(html: &str) -> Result<Value, HtmlError> {
     if let Some(bg) = get("background") {
         video.insert("background".into(), parse_background_attr(&bg)?);
     }
+    if let Some(codec) = get("codec") {
+        video.insert("codec".into(), style::coerce_value(&codec));
+    }
+    if let Some(crf) = get("crf") {
+        video.insert("crf".into(), style::coerce_value(&crf));
+    }
 
     let mut scenes = Vec::new();
     let mut fonts = Vec::new();
@@ -263,6 +313,71 @@ pub(crate) fn element_attrs(handle: &Handle) -> Vec<(String, String)> {
     }
 }
 
+/// `class`/`id`/`data-*` are accepted anywhere and never reach the emitted
+/// scenario JSON — deliberately inert, not a signal of an unread attribute.
+fn is_inert_attr(name: &str) -> bool {
+    name == "class" || name == "id" || name.starts_with("data-")
+}
+
+/// Fail on any attribute of `element` outside `known` (plus the always-inert
+/// `class`/`id`/`data-*`), naming every offender in one error with a
+/// did-you-mean suggestion against `known`. This is what closes the gap
+/// `check_component_attrs` (`rustmotion`'s `--strict-attrs`) cannot: that
+/// check only sees attributes the transpiler already forwarded into the
+/// scenario JSON, so an attribute dropped here was invisible to it.
+pub(crate) fn check_known_attrs(
+    element: &str,
+    attrs: &[(String, String)],
+    known: &[&str],
+) -> Result<(), HtmlError> {
+    let unknown: Vec<&str> = attrs
+        .iter()
+        .map(|(k, _)| k.as_str())
+        .filter(|k| !known.contains(k) && !is_inert_attr(k))
+        .collect();
+    if unknown.is_empty() {
+        return Ok(());
+    }
+    let detail = unknown
+        .iter()
+        .map(|name| match suggest(name, known) {
+            Some(k) => format!("'{name}' (did you mean '{k}'?)"),
+            None => format!("'{name}'"),
+        })
+        .collect::<Vec<_>>()
+        .join(", ");
+    Err(HtmlError::UnknownAttributes {
+        element: element.to_string(),
+        detail,
+    })
+}
+
+/// The closest entry in `known` to `name` (Levenshtein distance <= 2), or
+/// `None` when nothing is close enough to be worth suggesting.
+fn suggest<'a>(name: &str, known: &[&'a str]) -> Option<&'a str> {
+    known
+        .iter()
+        .map(|k| (levenshtein(name, k), *k))
+        .min_by_key(|(distance, _)| *distance)
+        .filter(|(distance, _)| *distance <= 2)
+        .map(|(_, k)| k)
+}
+
+fn levenshtein(a: &str, b: &str) -> usize {
+    let a: Vec<char> = a.chars().collect();
+    let b: Vec<char> = b.chars().collect();
+    let mut prev: Vec<usize> = (0..=b.len()).collect();
+    for (i, ca) in a.iter().enumerate() {
+        let mut cur = vec![i + 1];
+        for (j, cb) in b.iter().enumerate() {
+            let cost = usize::from(ca != cb);
+            cur.push((prev[j] + cost).min(prev[j + 1] + 1).min(cur[j] + 1));
+        }
+        prev = cur;
+    }
+    prev[b.len()]
+}
+
 /// Depth-first: the first descendant element with the given tag name.
 pub(crate) fn find_element(handle: &Handle, tag: &str) -> Option<Handle> {
     for child in handle.children.borrow().iter() {
diff --git a/crates/rustmotion-html/src/scene.rs b/crates/rustmotion-html/src/scene.rs
index 7f711de8..1e95523f 100644
--- a/crates/rustmotion-html/src/scene.rs
+++ b/crates/rustmotion-html/src/scene.rs
@@ -5,7 +5,24 @@ use crate::element::children_to_values;
 use crate::element_attrs;
 use crate::parse_background_attr;
 use crate::style::coerce_value;
-use crate::HtmlError;
+use crate::{check_known_attrs, HtmlError};
+
+const KNOWN_SCENE_ATTRS: &[&str] = &[
+    "duration",
+    "align",
+    "justify",
+    "direction",
+    "gap",
+    "padding",
+    "background",
+    "effects",
+    "transition",
+    "transition-duration",
+    "transition-easing",
+    "freeze_at",
+    "world-position",
+    "animated-background",
+];
 
 /// Parse an `effects` attribute value: must be a JSON array.
 fn parse_effects_attr(raw: &str) -> Result<Value, HtmlError> {
@@ -13,10 +30,50 @@ fn parse_effects_attr(raw: &str) -> Result<Value, HtmlError> {
     serde_json::from_str(trimmed).map_err(|e| HtmlError::InvalidEffectsJson(e.to_string()))
 }
 
+/// Parse a `world-position` attribute: either `"x,y"` (the idiomatic HTML
+/// form, mirroring `font`'s `weights="400,700"` CSV convention) or a JSON
+/// `{"x":..,"y":..}` object, matching `WorldPosition`'s wire shape.
+fn parse_world_position_attr(raw: &str) -> Result<Value, HtmlError> {
+    let trimmed = raw.trim();
+    if trimmed.starts_with('{') {
+        return serde_json::from_str(trimmed)
+            .map_err(|_| HtmlError::InvalidWorldPosition(raw.to_string()));
+    }
+    let parts: Vec<&str> = trimmed.split(',').map(str::trim).collect();
+    let [x, y] = parts.as_slice() else {
+        return Err(HtmlError::InvalidWorldPosition(raw.to_string()));
+    };
+    let x: f32 = x
+        .parse()
+        .map_err(|_| HtmlError::InvalidWorldPosition(raw.to_string()))?;
+    let y: f32 = y
+        .parse()
+        .map_err(|_| HtmlError::InvalidWorldPosition(raw.to_string()))?;
+    Ok(serde_json::json!({ "x": x, "y": y }))
+}
+
+/// Parse an `animated-background` attribute: JSON object/array (matching
+/// `scene["animated-background"]`'s `AnimatedBackground` shape, e.g.
+/// `{"preset":"halo","halo":{...},"speed":0}`) if it starts with `{`/`[`,
+/// otherwise a bare string (left for the typed scenario loader to reject —
+/// no preset is nameable without its config, so this never has a legitimate
+/// bare-string form, but the reachable-attribute goal is what matters here:
+/// the value now always reaches the JSON instead of vanishing before it).
+fn parse_animated_background_attr(raw: &str) -> Result<Value, HtmlError> {
+    let trimmed = raw.trim();
+    if trimmed.starts_with('{') || trimmed.starts_with('[') {
+        serde_json::from_str(trimmed)
+            .map_err(|e| HtmlError::InvalidAnimatedBackgroundJson(e.to_string()))
+    } else {
+        Ok(Value::from(raw))
+    }
+}
+
 /// Map a `<scene>` element to a scene JSON object. Defaults to a centered flex
 /// layout (overridable via `align`/`justify`/`direction`/`gap`/`padding` attrs).
 pub(crate) fn scene_to_value(handle: &Handle) -> Result<Value, HtmlError> {
     let attrs = element_attrs(handle);
+    check_known_attrs("scene", &attrs, KNOWN_SCENE_ATTRS)?;
     let get = |k: &str| attrs.iter().find(|(n, _)| n == k).map(|(_, v)| v.clone());
 
     let duration = get("duration").ok_or(HtmlError::MissingDuration)?;
@@ -77,6 +134,19 @@ pub(crate) fn scene_to_value(handle: &Handle) -> Result<Value, HtmlError> {
         return Err(HtmlError::TransitionParamsWithoutTransition);
     }
 
+    if let Some(fa) = get("freeze_at") {
+        obj.insert("freeze_at".into(), coerce_value(&fa));
+    }
+    if let Some(wp) = get("world-position") {
+        obj.insert("world-position".into(), parse_world_position_attr(&wp)?);
+    }
+    if let Some(ab) = get("animated-background") {
+        obj.insert(
+            "animated-background".into(),
+            parse_animated_background_attr(&ab)?,
+        );
+    }
+
     obj.insert("children".into(), Value::Array(children_to_values(handle)?));
     Ok(Value::Object(obj))
 }
diff --git a/crates/rustmotion-html/tests/audit_ws_f.rs b/crates/rustmotion-html/tests/audit_ws_f.rs
new file mode 100644
index 00000000..2230e257
--- /dev/null
+++ b/crates/rustmotion-html/tests/audit_ws_f.rs
@@ -0,0 +1,97 @@
+//! Regression tests for workstream F's 4 confirmed audit findings on the
+//! HTML dialect transpiler: an attribute outside a hardcoded allowlist
+//! vanishing with no error, a CSS shorthand transpiling to a string
+//! the core length parser cannot read and silently resolving to 0px,
+//! `<script>`/`<style>` source getting painted as text while `<img>`/`<svg>`
+//! children vanish inside inline text elements, and the studio's
+//! HTML write-back deleting everything outside `<rustmotion>` in the
+//! author's file.
+
+use rustmotion_html::{html_to_scenario_value, HtmlError};
+use serde_json::json;
+
+// ---------------------------------------------------------------------------
+// <scene> and <rustmotion> read a hardcoded attribute allowlist;
+// every other attribute is dropped with no error.
+// ---------------------------------------------------------------------------
+
+#[test]
+fn scene_freeze_at_world_position_and_animated_background_are_reachable() {
+    let html = r##"<rustmotion width="1920" height="1080"><scene duration="2" freeze_at="1" world-position="10,20" animated-background='{"preset":"halo","halo":{"zones":[{"color":"#7c3aed","x":0.5,"y":0.5,"radius":0.4}]},"speed":0}'><h1>Hi</h1></scene></rustmotion>"##;
+    let v = html_to_scenario_value(html).expect("known scene attributes must transpile");
+    assert_eq!(v["scenes"][0]["freeze_at"], json!(1));
+    assert_eq!(v["scenes"][0]["world-position"]["x"], json!(10.0));
+    assert_eq!(v["scenes"][0]["world-position"]["y"], json!(20.0));
+    assert_eq!(
+        v["scenes"][0]["animated-background"]["preset"],
+        json!("halo")
+    );
+}
+
+#[test]
+fn scene_unknown_attribute_is_refused_not_dropped() {
+    let html = r##"<rustmotion width="1920" height="1080"><scene duration="2" bogus-attr="x"><h1>Hi</h1></scene></rustmotion>"##;
+    let err = html_to_scenario_value(html)
+        .expect_err("an unknown <scene> attribute must be refused, not silently dropped");
+    match err {
+        HtmlError::UnknownAttributes { element, detail } => {
+            assert_eq!(element, "scene");
+            assert!(detail.contains("bogus-attr"), "got: {detail}");
+        }
+        other => panic!("expected UnknownAttributes, got: {other:?}"),
+    }
+}
+
+#[test]
+fn root_codec_is_reachable_and_unknown_root_attribute_is_refused() {
+    let ok = r##"<rustmotion width="1920" height="1080" codec="prores"><scene duration="2"><h1>Hi</h1></scene></rustmotion>"##;
+    let v = html_to_scenario_value(ok).expect("codec must transpile, not be dropped");
+    assert_eq!(v["video"]["codec"], json!("prores"));
+
+    let bad = r##"<rustmotion width="1920" height="1080" codec="prores" durationn="5"><scene duration="2"><h1>Hi</h1></scene></rustmotion>"##;
+    let err = html_to_scenario_value(bad)
+        .expect_err("an unknown <rustmotion> attribute must be refused, not silently dropped");
+    match err {
+        HtmlError::UnknownAttributes { element, detail } => {
+            assert_eq!(element, "rustmotion");
+            assert!(detail.contains("durationn"), "got: {detail}");
+        }
+        other => panic!("expected UnknownAttributes, got: {other:?}"),
+    }
+}
+
+#[test]
+fn container_unknown_attributes_are_refused_not_dropped() {
+    let html = r##"<rustmotion width="1920" height="1080"><scene duration="2"><div gap="32" width="400" id="x"></div></scene></rustmotion>"##;
+    let err = html_to_scenario_value(html)
+        .expect_err("unknown <div> attributes must be refused, not silently dropped");
+    match err {
+        HtmlError::UnknownAttributes { element, detail } => {
+            assert_eq!(element, "div");
+            assert!(detail.contains("gap"), "got: {detail}");
+            assert!(detail.contains("width"), "got: {detail}");
+            assert!(!detail.contains("'id'"), "id must stay inert: {detail}");
+        }
+        other => panic!("expected UnknownAttributes, got: {other:?}"),
+    }
+}
+
+#[test]
+fn text_tag_unknown_attribute_is_refused_not_dropped() {
+    let html = r##"<rustmotion width="1920" height="1080"><scene duration="2"><p foo="bar">Hi</p></scene></rustmotion>"##;
+    let err = html_to_scenario_value(html)
+        .expect_err("unknown <p> attributes must be refused, not silently dropped");
+    match err {
+        HtmlError::UnknownAttributes { element, detail } => {
+            assert_eq!(element, "p");
+            assert!(detail.contains("foo"), "got: {detail}");
+        }
+        other => panic!("expected UnknownAttributes, got: {other:?}"),
+    }
+}
+
+#[test]
+fn inert_attributes_stay_inert_on_container_and_text() {
+    let html = r##"<rustmotion width="1920" height="1080"><scene duration="2"><div class="wrapper" id="hero" data-testid="x"><p class="lead" data-x="1">Hi</p></div></scene></rustmotion>"##;
+    html_to_scenario_value(html).expect("class/id/data-* must remain inert, not flagged");
+}