diff --git a/docs/gpu-set-font-framing.md b/docs/gpu-set-font-framing.md
index 713afe1..b39b836 100644
--- a/docs/gpu-set-font-framing.md
+++ b/docs/gpu-set-font-framing.md
@@ -1,6 +1,7 @@
 # GPU font preference — framing (Arc 4 stage 2, `pmacs.gpu.set_font`)
 
-**Revision 4 — 2026-07-15. Status: awaiting review.**
+**Revision 4 — 2026-07-15. Status: implemented on branch
+`gpu-set-font` (protocol v17); awaiting PR review.**
 
 Revision 4 (framing round 3, findings 1–5): caret preservation is now
 VISUAL-RUN aware rather than source-line-only. The code buffer keeps a
diff --git a/docs/pmacs-gpu-design.md b/docs/pmacs-gpu-design.md
index 61d19e8..c7982e4 100644
--- a/docs/pmacs-gpu-design.md
+++ b/docs/pmacs-gpu-design.md
@@ -289,14 +289,21 @@ override.**
   classified as a small finding under rule (iii) and absorbed; the
   bundled `fonts/OFL.txt` is shipped alongside the TTF as required
   by the OFL.
-- Lua override: `pmacs.gpu.set_font(path)` or similar (precise binding
-  shape decided session 2).
+- Lua override: **landed** as `pmacs.gpu.set_font { family?, size? }`
+  (Arc 4 stage 2, `docs/gpu-set-font-framing.md`) — a family NAME
+  resolved frontend-locally against the sanitized font database, not
+  a path.
 - Missing-glyph fallback: tofu (replacement character `U+FFFD`).
   Explicit non-goal to ship a sophisticated fallback chain in v0.1.
   If real users hit this, it's v0.2+ scope.
 
 The bundled-default-plus-override shape means v0.1 works without
-configuration; future customization needs no wire-protocol changes.
+configuration. **Correction (Arc 4 stage 2):** this section originally
+claimed future customization would need no wire-protocol change, but
+the preference lives daemon-side (init.lua runs in the daemon, and
+every attaching GPU must render consistently), so customization
+shipped as the `FontFacts` fact at protocol v17 —
+`docs/gpu-set-font-framing.md` is the design of record.
 
 ## Rhythm
 
diff --git a/docs/semantic-frontend-protocol.md b/docs/semantic-frontend-protocol.md
index 3258fb7..66c2baf 100644
--- a/docs/semantic-frontend-protocol.md
+++ b/docs/semantic-frontend-protocol.md
@@ -126,8 +126,11 @@ invalidating its per-buffer emission baselines whenever it writes a
 snapshot, so the frontend's post-snapshot viewport declaration
 receives authoritative re-sends even when nothing changed
 daemon-side (the unchanged-generation A → B → A revisit). Bufferless
-facts (`ThemeFacts`, the minibuffer prompt) and per-frontend state
-(the gutter mode) survive snapshots on both sides, and the
+facts (`ThemeFacts`, `FontFacts`, the minibuffer prompt) and
+per-frontend state (the gutter mode) survive snapshots on both sides
+(frontend-locally the normalized code scroll — a caret-follow view
+residual — is buffer-scoped and resets, while the resolved font and
+derived metrics survive), and the
 instance's stale-store diagnostic-count freeze is store knowledge,
 not session state — the re-sent `StatusFacts` after a snapshot
 carries the frozen counts, never zeros, including for a session
@@ -245,6 +248,28 @@ ResourceOffer {
 ThemeFacts {
     faces: Vec<ThemeFace>, // { name: String, style: Style }, sorted by name
 },
+
+/// The GLOBAL font preference (protocol v17, Arc 4 stage 2,
+/// docs/gpu-set-font-framing.md), written by `pmacs.gpu.set_font`.
+/// Bufferless and authoritative per attachment: every session's
+/// first frame after viewport declaration carries the current
+/// preference — the all-default `(None, None)` included, never
+/// inferred from silence — and it is epoch-gated/cached-compare
+/// suppressed thereafter, so an unchanged preference costs one
+/// small message per attachment. `BufferSnapshot` resets never
+/// touch it on either side. The daemon relays a PREFERENCE only
+/// (no pixels): the frontend resolves the family locally
+/// (monospace-gated, total fallback to its sanitized default) and
+/// owns every metric consequence; sizes travel as integer
+/// hundredths of a logical pixel (1600 = 16.0, validated to
+/// 600..=7200 on BOTH sides — the receiver fails closed on
+/// out-of-range wire values). Daemon-gated `>= 17`; appended as
+/// the FINAL variant — postcard discriminants are ordinal, and the
+/// ThemeFacts byte pin above guards this placement.
+FontFacts {
+    family: Option<String>,     // None = the frontend's default family
+    size_centi_px: Option<u32>, // None = the frontend's default size
+},
 ```
 
 Each family member diffs against the previous frame the same way
diff --git a/src/lua_bindings/mod.rs b/src/lua_bindings/mod.rs
index 5afe4da..374e3d4 100644
--- a/src/lua_bindings/mod.rs
+++ b/src/lua_bindings/mod.rs
@@ -7559,9 +7559,6 @@ pub fn install_process(lua: &Lua, supervisor: &SharedProcessSupervisor) -> mlua:
     Ok(())
 }
 
-/// Build a fresh [`ProcessSupervisor`] and install
-/// `pmacs.process.*` over it. Mirrors [`make_async_runtime`] /
-/// [`make_syntax_registry`] in shape.
 /// `pmacs.gpu.*` — GPU frontend preferences (Arc 4 stage 2, framing
 /// Q#F2). Installs the module and returns the shared preference
 /// handle the `semantic_render` producer reads. Called from
@@ -7677,6 +7674,9 @@ fn validate_font_size(size: f64) -> mlua::Result<u32> {
     Ok((size * 100.0).round() as u32)
 }
 
+/// Build a fresh [`ProcessSupervisor`] and install
+/// `pmacs.process.*` over it. Mirrors [`make_async_runtime`] /
+/// [`make_syntax_registry`] in shape.
 pub fn make_process_supervisor(lua: &Lua) -> mlua::Result<SharedProcessSupervisor> {
     let supervisor = Rc::new(RefCell::new(ProcessSupervisor::new()));
     install_process(lua, &supervisor)?;
diff --git a/tests/gpu_font_acceptance.rs b/tests/gpu_font_acceptance.rs
new file mode 100644
index 0000000..264f25d
--- /dev/null
+++ b/tests/gpu_font_acceptance.rs
@@ -0,0 +1,492 @@
+// gpu_font_acceptance.rs --- gpu-set-font Arc 4 stage 2 acceptance
+// (docs/gpu-set-font-framing.md, acceptance items 2–7; item 1's pins
+// live in src/protocol.rs, item 8's TUI drop arm is a unit in
+// src/frontend.rs, items 9–14 and 16–19 are GPU routes in pmacs-gpu's
+// headless suite, and item 15 is the docs themselves).
+
+//! The `pmacs.gpu.set_font` preference + the `FontFacts` wire channel
+//! (protocol v17).
+//!
+//! Wire claims drive a `SemanticRenderState` frame by frame (the
+//! `ThemeFacts` discipline: authoritative per attachment, epoch-gated,
+//! silent when unchanged); the Lua contract is exercised against the
+//! real `pmacs.gpu` module installed by `EditorState::new`; the
+//! version gate exercises a real daemon; init.lua reachability goes
+//! through the real `load_user_config_at`.
+
+use pmacs::editor::EditorState;
+use pmacs::protocol::{ByteRange, FrontendId, InstanceMessage};
+use pmacs::semantic_render::SemanticRenderState;
+
+#[cfg(feature = "crdt")]
+mod common;
+
+// ---------------------------------------------------------------------------
+// Harness (theme_faces_acceptance conventions)
+// ---------------------------------------------------------------------------
+
+fn exec(s: &EditorState, src: &str) {
+    s.lua_host.lua().load(src.to_string()).exec().unwrap();
+}
+
+fn exec_err(s: &EditorState, src: &str) -> mlua::Error {
+    s.lua_host
+        .lua()
+        .load(src.to_string())
+        .exec()
+        .expect_err("chunk must error")
+}
+
+fn eval<T: mlua::FromLuaMulti>(s: &EditorState, src: &str) -> T {
+    s.lua_host.lua().load(src.to_string()).eval().unwrap()
+}
+
+/// Fresh editor with LSP spawning disabled.
+fn editor() -> EditorState {
+    let s = EditorState::new();
+    exec(&s, "pmacs.lsp.config = {}");
+    s
+}
+
+fn active_buffer(state: &EditorState) -> pmacs::buffer::BufferId {
+    state.core.borrow().active_window().buffer_id
+}
+
+fn semantic(state: &EditorState) -> SemanticRenderState {
+    let buffer_id = active_buffer(state);
+    let mut s = SemanticRenderState::new(FrontendId::LOCAL);
+    s.set_viewport(
+        buffer_id,
+        ByteRange {
+            start: 0,
+            end: 1 << 20,
+        },
+        0,
+    );
+    s
+}
+
+fn font_facts_of(msgs: &[InstanceMessage]) -> Option<(Option<String>, Option<u32>)> {
+    msgs.iter().find_map(|m| match m {
+        InstanceMessage::FontFacts {
+            family,
+            size_centi_px,
+        } => Some((family.clone(), *size_centi_px)),
+        _ => None,
+    })
+}
+
+fn font_facts_count(msgs: &[InstanceMessage]) -> usize {
+    msgs.iter()
+        .filter(|m| matches!(m, InstanceMessage::FontFacts { .. }))
+        .count()
+}
+
+/// The daemon-side preference triple `(family, size_centi_px, epoch)`.
+fn pref_of(state: &EditorState) -> (Option<String>, Option<u32>, u64) {
+    let pref = state.font_pref.lock().expect("font pref lock");
+    (pref.family.clone(), pref.size_centi_px, pref.epoch)
+}
+
+// ---------------------------------------------------------------------------
+// 2 — authoritative default per attachment; unchanged ticks silent;
+//     late joiner receives the current preference
+// ---------------------------------------------------------------------------
+
+#[test]
+fn first_frame_ships_the_authoritative_default_and_then_stays_silent() {
+    let state = editor();
+    let mut sem = semantic(&state);
+    let first = sem.render_frame(&state);
+    assert_eq!(
+        font_facts_of(&first),
+        Some((None, None)),
+        "a fresh attachment's first frame carries the REAL (None, None) default — \
+         never inferred from silence"
+    );
+    for tick in 0..3 {
+        let next = sem.render_frame(&state);
+        assert_eq!(
+            font_facts_count(&next),
+            0,
+            "unchanged tick {tick} must be FontFacts-silent"
+        );
+    }
+    // `state` untouched since the set below — a late-joining second
+    // session receives the current preference without any mutation
+    // post-attach.
+    exec(
+        &state,
+        r#"pmacs.gpu.set_font { family = "Iosevka", size = 18 }"#,
+    );
+    let mut late = semantic(&state);
+    let joined = late.render_frame(&state);
+    assert_eq!(
+        font_facts_of(&joined),
+        Some((Some("Iosevka".to_owned()), Some(1800))),
+        "a late joiner's first frame carries the current preference"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// 3 — live re-ship: one FontFacts on the next frame; an identical
+//     re-set advances the epoch without emitting
+// ---------------------------------------------------------------------------
+
+#[test]
+fn set_font_reships_once_and_identical_resets_advance_the_epoch_silently() {
+    let state = editor();
+    let mut sem = semantic(&state);
+    let _ = sem.render_frame(&state);
+    exec(&state, "pmacs.gpu.set_font { size = 18 }");
+    let next = sem.render_frame(&state);
+    assert_eq!(
+        font_facts_count(&next),
+        1,
+        "a mid-session set emits exactly one FontFacts on the next frame"
+    );
+    assert_eq!(font_facts_of(&next), Some((None, Some(1800))));
+    let (_, _, epoch_before) = pref_of(&state);
+    exec(&state, "pmacs.gpu.set_font { size = 18 }");
+    let (_, _, epoch_after) = pref_of(&state);
+    assert_eq!(
+        epoch_after,
+        epoch_before + 1,
+        "an identical re-set still advances the epoch (caches advance on \
+         computation, Q#TH6)"
+    );
+    let silent = sem.render_frame(&state);
+    assert_eq!(
+        font_facts_count(&silent),
+        0,
+        "an identical payload does not re-emit"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// 4 — snapshot survival, producer side: the buffer-baseline reset
+//     re-ships buffer facts but never the bufferless FontFacts
+// ---------------------------------------------------------------------------
+
+#[test]
+fn buffer_snapshot_reset_never_reships_font_facts() {
+    let state = editor();
+    exec(&state, "pmacs.gpu.set_font { size = 20 }");
+    let buffer_id = active_buffer(&state);
+    let mut sem = semantic(&state);
+    let first = sem.render_frame(&state);
+    assert_eq!(
+        font_facts_of(&first),
+        Some((None, Some(2000))),
+        "precondition: the preference shipped on the first frame"
+    );
+    let has_status = |msgs: &[InstanceMessage]| {
+        msgs.iter()
+            .any(|m| matches!(m, InstanceMessage::StatusFacts { .. }))
+    };
+    assert!(has_status(&first), "precondition: buffer facts shipped too");
+    // The daemon wrote a BufferSnapshot for this buffer (an A → B → A
+    // revisit): every BUFFER-scoped baseline resets…
+    sem.on_buffer_snapshot_sent(buffer_id);
+    let after = sem.render_frame(&state);
+    assert!(
+        has_status(&after),
+        "the reset re-ships the buffer's facts on the next frame"
+    );
+    // …but the global font baseline survives: the new buffer shapes
+    // under the same preference without a redundant global fact.
+    assert_eq!(
+        font_facts_count(&after),
+        0,
+        "FontFacts is bufferless — the snapshot reset must not touch it"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// 5 — the daemon version gate (v16 peer never receives FontFacts)
+// ---------------------------------------------------------------------------
+
+#[cfg(feature = "crdt")]
+#[test]
+fn v16_peer_never_receives_font_facts_and_v17_does() {
+    use common::daemon::{TestDaemon, build_default_caps};
+    use pmacs::cell::CellSize;
+    use pmacs::protocol::{AttachRequest, FrontendCapabilities, FrontendEvent, Hello};
+    use pmacs::transport::{read_message, write_message};
+    use std::time::{Duration, Instant};
+
+    fn semantic_caps() -> FrontendCapabilities {
+        FrontendCapabilities {
+            multi_frontend: true,
+            crdt_replica: true,
+            semantic_render: true,
+            ..build_default_caps()
+        }
+    }
+
+    /// Attach a semantic session at `version`, declare a viewport,
+    /// and report `(saw_font_facts, saw_style_spans)` within the
+    /// deadline.
+    fn probe(daemon: &TestDaemon, version: u32) -> (bool, bool) {
+        let mut stream = daemon.connect();
+        stream
+            .set_read_timeout(Some(Duration::from_millis(250)))
+            .unwrap();
+        let hello: Hello = read_message(&mut stream).expect("read Hello");
+        let fid = hello.assigned_frontend_id;
+        write_message(
+            &mut stream,
+            &AttachRequest {
+                protocol_version: version,
+                frontend_capabilities: semantic_caps(),
+                initial_size: CellSize::new(24, 80),
+            },
+        )
+        .expect("write AttachRequest");
+        let mut buf = None;
+        let learn_by = Instant::now() + Duration::from_secs(2);
+        while Instant::now() < learn_by && buf.is_none() {
+            if let Ok(InstanceMessage::BufferSnapshot { buffer_id, .. }) =
+                read_message::<InstanceMessage>(&mut stream)
+            {
+                buf = Some(buffer_id);
+            }
+        }
+        let buffer_id = buf.expect("received a BufferSnapshot");
+        write_message(
+            &mut stream,
+            &FrontendEvent::Viewport {
+                frontend_id: fid,
+                buffer_id,
+                visible: ByteRange {
+                    start: 0,
+                    end: 4096,
+                },
+                generation: 0,
+            },
+        )
+        .expect("write Viewport");
+        let deadline = Instant::now() + Duration::from_secs(3);
+        let (mut saw_facts, mut saw_spans) = (false, false);
+        while Instant::now() < deadline && !(saw_facts && saw_spans) {
+            match read_message::<InstanceMessage>(&mut stream) {
+                Ok(InstanceMessage::FontFacts { .. }) => saw_facts = true,
+                Ok(InstanceMessage::StyleSpans { .. }) => saw_spans = true,
+                Ok(_) | Err(_) => {}
+            }
+        }
+        (saw_facts, saw_spans)
+    }
+
+    let daemon = TestDaemon::spawn();
+    let (v17_facts, v17_spans) = probe(&daemon, 17);
+    assert!(v17_spans, "a v17 semantic session receives StyleSpans");
+    assert!(
+        v17_facts,
+        "a v17 semantic session receives the authoritative FontFacts"
+    );
+    let (v16_facts, v16_spans) = probe(&daemon, 16);
+    assert!(v16_spans, "a v16 peer still receives StyleSpans");
+    assert!(
+        !v16_facts,
+        "the daemon skip arm must keep FontFacts off a v16 wire"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// 6 — the Lua contract: strict plain data, all-or-nothing
+// ---------------------------------------------------------------------------
+
+#[test]
+fn set_font_rejects_bad_sizes_naming_the_field_and_nothing_lands() {
+    let state = editor();
+    let mut sem = semantic(&state);
+    let _ = sem.render_frame(&state);
+    let before = pref_of(&state);
+    for bad in [
+        "pmacs.gpu.set_font { size = 5.999 }", // must error, not round into range
+        "pmacs.gpu.set_font { size = 72.01 }",
+        "pmacs.gpu.set_font { size = 0 }",
+        "pmacs.gpu.set_font { size = -16 }",
+        "pmacs.gpu.set_font { size = 0/0 }",  // NaN
+        "pmacs.gpu.set_font { size = 1/0 }",  // +inf
+        "pmacs.gpu.set_font { size = '16' }", // non-number
+    ] {
+        let err = exec_err(&state, bad);
+        assert!(
+            err.to_string().contains("`size`"),
+            "{bad}: the error names the offending field, got: {err}"
+        );
+    }
+    assert_eq!(pref_of(&state), before, "no failed set may land");
+    let silent = sem.render_frame(&state);
+    assert_eq!(
+        font_facts_count(&silent),
+        0,
+        "no failed set may emit on the wire"
+    );
+}
+
+#[test]
+fn set_font_rejects_bad_families_and_unknown_keys_by_name() {
+    let state = editor();
+    let err = exec_err(&state, "pmacs.gpu.set_font { family = '' }");
+    assert!(
+        err.to_string().contains("`family`"),
+        "empty family names the field: {err}"
+    );
+    let err = exec_err(&state, "pmacs.gpu.set_font { family = 12 }");
+    assert!(
+        err.to_string().contains("`family`"),
+        "non-string family names the field: {err}"
+    );
+    let err = exec_err(&state, "pmacs.gpu.set_font { size = 18, sise = 20 }");
+    assert!(
+        err.to_string().contains("`sise`"),
+        "an unknown key is rejected by NAME: {err}"
+    );
+    assert_eq!(
+        pref_of(&state),
+        (None, None, 0),
+        "every rejected shape leaves the preference untouched"
+    );
+}
+
+#[test]
+fn set_font_never_consults_metatables() {
+    let state = editor();
+    // A hostile `__index` that answers every lookup: raw reads must
+    // never see its values, and raw iteration must never invoke it.
+    exec(
+        &state,
+        r#"
+        _G.__mt_hits = 0
+        local spec = setmetatable({ size = 18 }, {
+            __index = function(_, _)
+                _G.__mt_hits = _G.__mt_hits + 1
+                return "Injected Family"
+            end,
+            __pairs = function()
+                _G.__mt_hits = _G.__mt_hits + 1
+                return function() return nil end
+            end,
+        })
+        pmacs.gpu.set_font(spec)
+        "#,
+    );
+    let hits: i64 = eval(&state, "return _G.__mt_hits");
+    assert_eq!(hits, 0, "metatables are never invoked");
+    assert_eq!(
+        pref_of(&state),
+        (None, Some(1800), 1),
+        "the metatable's `family` answer must NOT be injected — only the \
+         raw `size` landed"
+    );
+}
+
+#[test]
+fn set_font_quantizes_both_sides_of_a_hundredth_and_empty_resets() {
+    let state = editor();
+    exec(&state, "pmacs.gpu.set_font { size = 15.994 }");
+    assert_eq!(pref_of(&state).1, Some(1599), "15.994 rounds DOWN");
+    exec(&state, "pmacs.gpu.set_font { size = 15.996 }");
+    assert_eq!(pref_of(&state).1, Some(1600), "15.996 rounds UP");
+    // Boundary values are in range and quantize exactly.
+    exec(&state, "pmacs.gpu.set_font { size = 6 }");
+    assert_eq!(pref_of(&state).1, Some(600));
+    exec(&state, "pmacs.gpu.set_font { size = 72 }");
+    assert_eq!(pref_of(&state).1, Some(7200));
+    exec(
+        &state,
+        r#"pmacs.gpu.set_font { family = "Iosevka", size = 18 }"#,
+    );
+    exec(&state, "pmacs.gpu.set_font {}");
+    let (family, size, _) = pref_of(&state);
+    assert_eq!(
+        (family, size),
+        (None, None),
+        "set_font {{}} resets BOTH axes to the frontend default"
+    );
+}
+
+#[test]
+fn font_getter_returns_a_fresh_quantized_plain_table() {
+    let state = editor();
+    exec(&state, "pmacs.gpu.set_font { size = 15.996 }");
+    let (size, fresh, no_family): (f64, bool, bool) = eval(
+        &state,
+        r"
+        local a = pmacs.gpu.font()
+        local b = pmacs.gpu.font()
+        a.size = 999  -- scribbling on the returned table…
+        local c = pmacs.gpu.font()
+        return c.size, rawequal(a, b) == false, c.family == nil
+        ",
+    );
+    assert!(
+        (size - 16.0).abs() < f64::EPSILON,
+        "the getter reports the QUANTIZED value (1600 → 16.0), got {size}"
+    );
+    assert!(
+        fresh,
+        "each call returns a fresh table, never a stored handle"
+    );
+    assert!(
+        no_family,
+        "an unset axis is absent, and scribbles don't stick"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// 7 — init.lua reachability: the module installs BEFORE user config
+// ---------------------------------------------------------------------------
+
+#[test]
+fn init_lua_set_font_lands_in_the_preference_the_first_frame_reads() {
+    use pmacs::config::load_user_config_at;
+    use pmacs::lua::LuaHost;
+
+    let dir = tempfile::TempDir::new().expect("tempdir");
+    std::fs::write(
+        dir.path().join("init.lua"),
+        r#"pmacs.gpu.set_font { family = "Iosevka", size = 18 }"#,
+    )
+    .expect("write init.lua");
+
+    let mut host = LuaHost::new().expect("LuaHost::new");
+    // Mirror `EditorState::new`'s ordering: the pmacs.gpu module
+    // installs BEFORE user config runs (src/editor.rs), so an
+    // init.lua set_font lands in the same state the first
+    // attachment's producer reads.
+    let handle = pmacs::lua_bindings::make_font_pref(host.lua()).expect("install pmacs.gpu");
+    load_user_config_at(&mut host, dir.path());
+    host.set_init_complete();
+    assert!(
+        host.errors().is_empty(),
+        "init.lua produced errors: {:?}",
+        host.errors()
+    );
+    let pref = handle.lock().expect("font pref lock");
+    assert_eq!(pref.family.as_deref(), Some("Iosevka"));
+    assert_eq!(pref.size_centi_px, Some(1800));
+    assert_eq!(pref.epoch, 1, "exactly the init.lua set landed");
+}
+
+/// The producer half of item 7: a preference already in place before
+/// the first attachment (the init.lua timing) ships on that
+/// attachment's FIRST frame.
+#[test]
+fn preference_set_before_attach_ships_on_the_first_frame() {
+    let state = editor();
+    exec(
+        &state,
+        r#"pmacs.gpu.set_font { family = "Iosevka", size = 18 }"#,
+    );
+    let mut sem = semantic(&state);
+    let first = sem.render_frame(&state);
+    assert_eq!(
+        font_facts_of(&first),
+        Some((Some("Iosevka".to_owned()), Some(1800))),
+        "the first frame ships the pre-attach preference"
+    );
+}