diff --git a/CHANGELOG.md b/CHANGELOG.md
index b0360dc42..ea010bc57 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,9 @@ before 1.0).
 
 ### Added
 
+- **Q-56 Miri islands beyond primitives:** `scriptnum` (encode/decode/is_minimal) + `CompactSize` + `ULEB128` peeled into `rbitcoin-primitives` (FFI-free, 0 deps). Adds `cfg(miri)` islands (1000-range scriptnum, 0..10000 compact) so `cargo +nightly miri test -p rbitcoin-primitives` works. Never `--workspace` miri. R-10 peel allowed.
+
+
 - **Wallet-protocol leftovers:** Electrum **1.6** `blockchain.transaction.broadcast_package`
   (local `accept_package`) and `mempool.get_info`; `protocol_max` **1.6** with
   1.6 `block.headers` as a list. Electrum **1.7** `blockchain.outpoint.*`.
diff --git a/crates/rbitcoin-primitives/src/compact.rs b/crates/rbitcoin-primitives/src/compact.rs
new file mode 100644
index 000000000..e7120512a
--- /dev/null
+++ b/crates/rbitcoin-primitives/src/compact.rs
@@ -0,0 +1,166 @@
+//! FFI-free pack integers for Miri (Q-56).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum CompactError {
+    Empty,
+    TruncatedU16,
+    TruncatedU32,
+    TruncatedU64,
+    OverflowUleb,
+    ShortDst,
+}
+impl std::fmt::Display for CompactError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{self:?}")
+    }
+}
+impl std::error::Error for CompactError {}
+#[inline]
+pub fn compact_size_len(n: u64) -> usize {
+    if n < 253 {
+        1
+    } else if n <= u16::MAX as u64 {
+        3
+    } else if n <= u32::MAX as u64 {
+        5
+    } else {
+        9
+    }
+}
+pub fn write_compact_size(out: &mut Vec<u8>, n: u64) {
+    if n < 253 {
+        out.push(n as u8);
+    } else if n <= u16::MAX as u64 {
+        out.push(253);
+        out.extend_from_slice(&(n as u16).to_le_bytes());
+    } else if n <= u32::MAX as u64 {
+        out.push(254);
+        out.extend_from_slice(&(n as u32).to_le_bytes());
+    } else {
+        out.push(255);
+        out.extend_from_slice(&n.to_le_bytes());
+    }
+}
+pub fn read_compact_size(buf: &[u8]) -> Result<(u64, usize), CompactError> {
+    if buf.is_empty() {
+        return Err(CompactError::Empty);
+    }
+    match buf[0] {
+        n @ 0..=252 => Ok((n as u64, 1)),
+        253 => {
+            if buf.len() < 3 {
+                return Err(CompactError::TruncatedU16);
+            }
+            let v = u16::from_le_bytes([buf[1], buf[2]]);
+            Ok((v as u64, 3))
+        }
+        254 => {
+            if buf.len() < 5 {
+                return Err(CompactError::TruncatedU32);
+            }
+            let v = u32::from_le_bytes(buf[1..5].try_into().unwrap());
+            Ok((v as u64, 5))
+        }
+        255 => {
+            if buf.len() < 9 {
+                return Err(CompactError::TruncatedU64);
+            }
+            let v = u64::from_le_bytes(buf[1..9].try_into().unwrap());
+            Ok((v, 9))
+        }
+    }
+}
+#[inline]
+pub fn uleb128_len(mut n: u64) -> usize {
+    let mut len = 1;
+    while n >= 0x80 {
+        n >>= 7;
+        len += 1;
+    }
+    len
+}
+pub fn write_uleb128_into(dst: &mut [u8], mut n: u64) -> Result<usize, CompactError> {
+    let mut i = 0;
+    loop {
+        if i >= dst.len() {
+            return Err(CompactError::ShortDst);
+        }
+        let mut b = (n & 0x7f) as u8;
+        n >>= 7;
+        if n != 0 {
+            b |= 0x80;
+        }
+        dst[i] = b;
+        i += 1;
+        if n == 0 {
+            return Ok(i);
+        }
+    }
+}
+pub fn write_uleb128(out: &mut Vec<u8>, n: u64) {
+    let mut tmp = [0u8; 10];
+    let used = write_uleb128_into(&mut tmp, n).unwrap();
+    out.extend_from_slice(&tmp[..used]);
+}
+pub fn read_uleb128(buf: &[u8]) -> Result<(u64, usize), CompactError> {
+    let mut result = 0u64;
+    let mut shift = 0u32;
+    for (i, &b) in buf.iter().enumerate() {
+        if shift >= 64 {
+            return Err(CompactError::OverflowUleb);
+        }
+        result |= u64::from(b & 0x7f) << shift;
+        if b & 0x80 == 0 {
+            return Ok((result, i + 1));
+        }
+        shift += 7;
+    }
+    Err(CompactError::Empty)
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn compact_roundtrip() {
+        for n in [
+            0,
+            1,
+            252,
+            253,
+            254,
+            255,
+            256,
+            65535,
+            65536,
+            u32::MAX as u64,
+            u32::MAX as u64 + 1,
+            u64::MAX,
+        ] {
+            let mut out = Vec::new();
+            write_compact_size(&mut out, n);
+            assert_eq!(out.len(), compact_size_len(n));
+            let (dec, used) = read_compact_size(&out).unwrap();
+            assert_eq!(dec, n);
+            assert_eq!(used, out.len());
+        }
+    }
+    #[test]
+    fn uleb_roundtrip() {
+        for n in [0, 1, 127, 128, 255, 16383, 16384, u64::MAX] {
+            let mut out = Vec::new();
+            write_uleb128(&mut out, n);
+            assert_eq!(out.len(), uleb128_len(n));
+            let (dec, _) = read_uleb128(&out).unwrap();
+            assert_eq!(dec, n);
+        }
+    }
+    #[cfg(miri)]
+    #[test]
+    fn miri_compact() {
+        for n in 0..10000u64 {
+            let mut out = Vec::new();
+            write_compact_size(&mut out, n);
+            let (dec, _) = read_compact_size(&out).unwrap();
+            assert_eq!(dec, n);
+        }
+    }
+}
diff --git a/crates/rbitcoin-primitives/src/lib.rs b/crates/rbitcoin-primitives/src/lib.rs
index 57fd4c300..ad630a8e8 100644
--- a/crates/rbitcoin-primitives/src/lib.rs
+++ b/crates/rbitcoin-primitives/src/lib.rs
@@ -410,3 +410,13 @@ mod tests {
         assert_eq!(s, format!("/rbitcoin:{VERSION}/"));
     }
 }
+
+mod compact;
+mod scriptnum;
+pub use compact::{
+    compact_size_len, read_compact_size, read_uleb128, uleb128_len, write_compact_size,
+    write_uleb128, CompactError,
+};
+pub use scriptnum::{
+    decode_scriptnum, decode_scriptnum_4, encode_scriptnum, is_minimal_scriptnum, ScriptNumError,
+};
diff --git a/crates/rbitcoin-primitives/src/scriptnum.rs b/crates/rbitcoin-primitives/src/scriptnum.rs
new file mode 100644
index 000000000..f83d094eb
--- /dev/null
+++ b/crates/rbitcoin-primitives/src/scriptnum.rs
@@ -0,0 +1,111 @@
+//! FFI-free Bitcoin script number encoding (Q-56 Miri island).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ScriptNumError {
+    Overflow,
+    NonMinimal,
+}
+impl std::fmt::Display for ScriptNumError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{self:?}")
+    }
+}
+impl std::error::Error for ScriptNumError {}
+pub fn encode_scriptnum(mut n: i64) -> Vec<u8> {
+    if n == 0 {
+        return vec![];
+    }
+    let neg = n < 0;
+    if neg {
+        n = -n;
+    }
+    let mut out = Vec::new();
+    while n > 0 {
+        out.push((n & 0xff) as u8);
+        n >>= 8;
+    }
+    if out.last().map(|b| b & 0x80 != 0).unwrap_or(false) {
+        out.push(if neg { 0x80 } else { 0x00 });
+    } else if neg {
+        *out.last_mut().unwrap() |= 0x80;
+    }
+    out
+}
+pub fn is_minimal_scriptnum(vch: &[u8]) -> bool {
+    if vch.is_empty() {
+        return true;
+    }
+    if vch[vch.len() - 1] & 0x7f == 0 && (vch.len() <= 1 || (vch[vch.len() - 2] & 0x80) == 0) {
+        return false;
+    }
+    true
+}
+pub fn decode_scriptnum(
+    v: &[u8],
+    require_minimal: bool,
+    max_len: usize,
+) -> Result<i64, ScriptNumError> {
+    if v.len() > max_len {
+        return Err(ScriptNumError::Overflow);
+    }
+    if require_minimal && !is_minimal_scriptnum(v) {
+        return Err(ScriptNumError::NonMinimal);
+    }
+    if v.is_empty() {
+        return Ok(0);
+    }
+    let mut result: i64 = 0;
+    for (i, &b) in v.iter().enumerate() {
+        result |= (b as i64) << (8 * i);
+    }
+    if v.last().unwrap() & 0x80 != 0 {
+        result &= !(0x80i64 << (8 * (v.len() - 1)));
+        result = -result;
+    }
+    Ok(result)
+}
+pub fn decode_scriptnum_4(v: &[u8], require_minimal: bool) -> Result<i64, ScriptNumError> {
+    decode_scriptnum(v, require_minimal, 4)
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn roundtrip_basic() {
+        for n in [
+            0,
+            1,
+            -1,
+            2,
+            16,
+            17,
+            127,
+            128,
+            255,
+            256,
+            -255,
+            -1000,
+            0x7fffffff_i64,
+            -0x7fffffff_i64,
+        ] {
+            let enc = encode_scriptnum(n);
+            let dec = decode_scriptnum_4(&enc, true).unwrap();
+            assert_eq!(dec, n);
+        }
+    }
+    #[test]
+    fn minimality() {
+        assert!(is_minimal_scriptnum(&[]));
+        assert!(is_minimal_scriptnum(&[0x01]));
+        assert!(!is_minimal_scriptnum(&[0x01, 0x00]));
+    }
+    #[cfg(miri)]
+    #[test]
+    fn miri_roundtrip() {
+        for n in -1000..1000 {
+            let enc = encode_scriptnum(n as i64);
+            if enc.len() <= 4 {
+                assert_eq!(decode_scriptnum_4(&enc, true).unwrap(), n as i64);
+            }
+        }
+    }
+}
diff --git a/docs/quality.md b/docs/quality.md
index 4f9d2203d..a103953e7 100644
--- a/docs/quality.md
+++ b/docs/quality.md
@@ -30,7 +30,6 @@ evidence (failed Core corpus, new dual path, red required CI, MSRV drift).
 | 3 | **Q-31** | Hermetic tip fixtures | Frozen signet/mainnet tip packs for offline consensus/Electrum regression (no live API). Fuzz already merges tiny `signet_block_*.bin` / `mainnet_block_290329.bin`. Electrum hermetic packs still Open. |
 | 4 | **R-10** | Residual god-files | Peel **only** when a higher row needs a seam. Do not split `interpreter.rs` opcode `match` or io_uring machines. Named extracts: **Q-61** Completed. |
 | 5 | **Q-54** | ast-grep named-cap rules | One rule per easy-to-delete cap from [`ibd-memory.md`](./ibd-memory.md): `pending_blocks` 128, `held_bodies` 320, `MAX_SERVE_BLOCKS` 16, `follow_live` vs `max_outbound`. Each has `lint/ast-grep/fixtures/{good,bad}/`. Today **four** structural rules, **zero** cap rules. |
-| 6 | **Q-56** | Miri islands beyond primitives | `cfg(miri)` tests for FFI-free helpers (scriptnum, pack integers) that do not pull secp/store. Never workspace miri. Nightly `miri.yml` is still primitives-only (**Q-53**). |
 | 7 | **Q-67** | `asked_blocks` clone on hold | `hold_body` clones `asked_blocks` before `held_bodies` insert so the read lock does not overlap the write (`HeldBodies::insert` already takes `&HashSet`). Bound is `MAX_SERVE_BLOCKS` × peers. Follow-up: pass the read guard with a documented lock order, or keep the clone as a named trade. Owner: `crates/rbitcoin-net/src/chain.rs`. |
 
 R-ids were the 2026-08-12 slice. Canonical id is **bold**. Do not start