feat(pairing): delegated approval (§8b-1) — approve an unpaired device from the console

An identified-but-unpaired device that knocks on a pairing-required host is now
held as a pending request the operator approves from the web console — pairing it
with no PIN fetched out of band — instead of a flat reject.

- core: Hello gains an optional trailing device name (len u8 || UTF-8, ≤64,
  same trailing-back-compat pattern as compositor/gamepad/bitrate). client-rs
  --name sends it; the connector sends None (fingerprint-derived label).
- native_pairing: in-memory pending queue (note_pending dedups by fingerprint,
  evicts the least-recently-active past a 32 cap, 10-min TTL); approve_pending
  pins the fingerprint, deny drops it. Names are sanitized (strip control/ANSI/
  bidi — untrusted wire input); add()/remove() roll back in-memory on a persist
  failure; pairing clears any stale pending knock.
- m3: the require_pairing gate records the knock (sanitized label) before
  rejecting; anonymous (certless) clients record nothing.
- mgmt: GET /native/pending, POST /native/pending/{id}/approve (optional {name})
  and /deny; OpenAPI + tests; docs/api/openapi.json regenerated.
- web: a "Waiting for approval" section on the Pairing page (live-poll, Approve/
  Deny, error-surfaced via QueryState); en+de strings.
- Also completes an in-progress NativeClient Sync refactor (receivers behind
  per-plane mutexes) that was left half-applied in the tree.

Adversarially reviewed (4 lenses + 3-vote verify); the confirmed findings are
fixed here. Validated live on the GNOME box: knock (with a wire name, and a
malicious ANSI/bidi name that got neutralized) → pending → approve → the same
identity streams real video. Full workspace tests + clippy + fmt green; web tsc
clean. Roadmap §8b-1 marked done; §8b-2 (peer-push approval) is the client
follow-up. See docs-site pairing page.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/native_pairing.rs

@@ -47,10 +47,47 @@ struct Armed {
     expires_at: Option<Instant>,
 }
 
-/// Shared native-pairing state: the arming PIN window + the persistent trust store.
+/// An unpaired (but identified) device that knocked on a pairing-required host — held for
+/// **delegated approval** from the management console (roadmap §8b-1) instead of being silently
+/// forgotten. In-memory only: pending knocks don't survive a restart (the device just knocks
+/// again), and they expire after [`PENDING_TTL`].
+struct Pending {
+    id: u32,
+    name: String,
+    fp_hex: String,
+    requested_at: Instant,
+}
+
+#[derive(Default)]
+struct PendingState {
+    next_id: u32,
+    items: Vec<Pending>,
+}
+
+/// A pending-approval snapshot for the management API / web console.
+pub struct PendingRequest {
+    /// Per-process id used to address approve/deny (stable for the entry's lifetime).
+    pub id: u32,
+    /// Best-effort device label (the client's `Hello` name, else fingerprint-derived).
+    pub name: String,
+    /// Hex SHA-256 of the knocking client's certificate — what approval pins.
+    pub fingerprint: String,
+    /// Seconds since the (most recent) knock.
+    pub age_secs: u64,
+}
+
+/// Pending knocks older than this are dropped (the device retries; a stale entry shouldn't be
+/// approvable days later when the operator no longer remembers the context).
+const PENDING_TTL: Duration = Duration::from_secs(10 * 60);
+/// Cap on the pending list — a LAN scanner must not grow it unboundedly. Oldest entries drop.
+const PENDING_CAP: usize = 32;
+
+/// Shared native-pairing state: the arming PIN window + the persistent trust store + the
+/// pending-approval queue.
 pub struct NativePairing {
     arm: Mutex<Armed>,
     paired: Mutex<PairedState>,
+    pending: Mutex<PendingState>,
 }
 
 /// A snapshot for the management API / web console.
@@ -92,6 +129,48 @@ fn random_pin() -> String {
     format!("{:04}", rand::thread_rng().gen_range(0..10_000u32))
 }
 
+/// Sanitize a client-supplied device name before it's stored, listed, or logged. The name comes
+/// straight off the wire (the `Hello`/`PairRequest` of an *unpaired* device), so it's untrusted: a
+/// hostile LAN device could embed terminal escapes / control characters (log + console injection) or
+/// bidi overrides (`U+202E` etc.) to make a malicious device *look* like a trusted one in the
+/// approval UI. Strip C0/C1 controls and Unicode bidi/format controls, collapse whitespace, trim, and
+/// cap the length; an empty/all-control name falls back to a fingerprint-derived label.
+pub(crate) fn sanitize_device_name(name: &str, fp_hex: &str) -> String {
+    let cleaned: String = name
+        .chars()
+        .map(|c| if c == '\t' || c == '\n' { ' ' } else { c })
+        .filter(|&c| {
+            !c.is_control()
+                // Bidi/format controls that could spoof or reorder the displayed name.
+                && !('\u{202A}'..='\u{202E}').contains(&c) // LRE..RLO/PDF
+                && !('\u{2066}'..='\u{2069}').contains(&c) // LRI..PDI
+                && c != '\u{200E}' // LRM
+                && c != '\u{200F}' // RLM
+                && c != '\u{061C}' // ALM
+                && c != '\u{FEFF}' // BOM / zero-width no-break space
+        })
+        .collect();
+    // Collapse internal whitespace runs, trim, cap at the wire limit.
+    let collapsed = cleaned.split_whitespace().collect::<Vec<_>>().join(" ");
+    let mut trimmed = collapsed.as_str();
+    while trimmed.len() > NAME_MAX {
+        let mut cut = NAME_MAX;
+        while !trimmed.is_char_boundary(cut) {
+            cut -= 1;
+        }
+        trimmed = &trimmed[..cut];
+    }
+    let trimmed = trimmed.trim();
+    if trimmed.is_empty() {
+        format!("device {}", &fp_hex[..8.min(fp_hex.len())])
+    } else {
+        trimmed.to_string()
+    }
+}
+
+/// Max stored device-name length (matches the `Hello` wire cap, `quic::HELLO_NAME_MAX`).
+const NAME_MAX: usize = 64;
+
 impl NativePairing {
     /// Load the trust store. `store_path = None` uses the default config path. If `arm_at_start`
     /// (the CLI `--allow-pairing`/`--require-pairing` flags), arm immediately with `fixed_pin`
@@ -117,6 +196,7 @@ impl NativePairing {
         Ok(NativePairing {
             arm: Mutex::new(arm),
             paired: Mutex::new(PairedState { path, clients }),
+            pending: Mutex::new(PendingState::default()),
         })
     }
 
@@ -172,15 +252,33 @@ impl NativePairing {
         self.paired.lock().unwrap().clients.contains(fp_hex)
     }
 
-    /// Record a successful pairing (re-pairing the same fingerprint just updates the name).
+    /// Record a successful pairing (re-pairing the same fingerprint just updates the name —
+    /// matched case-insensitively, like every other fingerprint comparison here). The name is
+    /// sanitized (untrusted). On a persist failure the in-memory store is rolled back so it never
+    /// diverges from disk. Also clears any pending knock for this fingerprint (it's now paired).
     pub fn add(&self, name: &str, fp_hex: &str) -> Result<()> {
-        let mut p = self.paired.lock().unwrap();
-        p.clients.clients.retain(|c| c.fingerprint != fp_hex);
-        p.clients.clients.push(PairedClient {
-            name: name.to_string(),
-            fingerprint: fp_hex.to_string(),
-        });
-        save(&p)
+        let name = sanitize_device_name(name, fp_hex);
+        {
+            let mut p = self.paired.lock().unwrap();
+            let snapshot = p.clients.clients.clone(); // restore on a failed save
+            p.clients
+                .clients
+                .retain(|c| !c.fingerprint.eq_ignore_ascii_case(fp_hex));
+            p.clients.clients.push(PairedClient {
+                name,
+                fingerprint: fp_hex.to_string(),
+            });
+            if let Err(e) = save(&p) {
+                p.clients.clients = snapshot;
+                return Err(e);
+            }
+        }
+        // A device that knocked and is now paired shouldn't linger in the approval list.
+        let mut pending = self.pending.lock().unwrap();
+        pending
+            .items
+            .retain(|p| !p.fp_hex.eq_ignore_ascii_case(fp_hex));
+        Ok(())
     }
 
     /// The paired clients (for the management API's device list).
@@ -188,19 +286,122 @@ impl NativePairing {
         self.paired.lock().unwrap().clients.clients.clone()
     }
 
-    /// Remove a paired client by fingerprint. Returns whether one was removed.
+    /// Remove a paired client by fingerprint. Returns whether one was removed. On a persist
+    /// failure the in-memory store is rolled back (it never diverges from disk).
     pub fn remove(&self, fp_hex: &str) -> Result<bool> {
         let mut p = self.paired.lock().unwrap();
         let before = p.clients.clients.len();
+        let snapshot = p.clients.clients.clone();
         p.clients
             .clients
             .retain(|c| !c.fingerprint.eq_ignore_ascii_case(fp_hex));
         let removed = p.clients.clients.len() != before;
         if removed {
-            save(&p)?;
+            if let Err(e) = save(&p) {
+                p.clients.clients = snapshot;
+                return Err(e);
+            }
         }
         Ok(removed)
     }
+
+    // -- Delegated approval (roadmap §8b-1) --------------------------------
+
+    /// Drop expired pending knocks (called under the lock, mirroring [`Self::expire`]).
+    fn expire_pending(pending: &mut PendingState) {
+        pending
+            .items
+            .retain(|p| p.requested_at.elapsed() < PENDING_TTL);
+    }
+
+    /// Record an unpaired device's knock for delegated approval. Re-knocks from the same
+    /// fingerprint refresh the existing entry in place (same id; a connect-retry loop must not spam
+    /// the list); a fresh fingerprint gets a new id, evicting the **least-recently-active** entry
+    /// past [`PENDING_CAP`]. The name is sanitized (untrusted; see [`sanitize_device_name`]).
+    pub fn note_pending(&self, name: &str, fp_hex: &str) {
+        let name = sanitize_device_name(name, fp_hex);
+        let mut pending = self.pending.lock().unwrap();
+        Self::expire_pending(&mut pending);
+        if let Some(p) = pending
+            .items
+            .iter_mut()
+            .find(|p| p.fp_hex.eq_ignore_ascii_case(fp_hex))
+        {
+            p.requested_at = Instant::now();
+            p.name = name;
+            return;
+        }
+        if pending.items.len() >= PENDING_CAP {
+            // Evict the least-recently-active entry. NOT index 0: the in-place refresh above means
+            // Vec order no longer tracks recency, so pick the minimum `requested_at` explicitly.
+            if let Some(at) = pending
+                .items
+                .iter()
+                .enumerate()
+                .min_by_key(|(_, p)| p.requested_at)
+                .map(|(i, _)| i)
+            {
+                pending.items.remove(at);
+            }
+        }
+        let id = pending.next_id;
+        pending.next_id = pending.next_id.wrapping_add(1);
+        pending.items.push(Pending {
+            id,
+            name,
+            fp_hex: fp_hex.to_string(),
+            requested_at: Instant::now(),
+        });
+    }
+
+    /// The devices currently awaiting approval (for the management API).
+    pub fn pending(&self) -> Vec<PendingRequest> {
+        let mut pending = self.pending.lock().unwrap();
+        Self::expire_pending(&mut pending);
+        pending
+            .items
+            .iter()
+            .map(|p| PendingRequest {
+                id: p.id,
+                name: p.name.clone(),
+                fingerprint: p.fp_hex.clone(),
+                age_secs: p.requested_at.elapsed().as_secs(),
+            })
+            .collect()
+    }
+
+    /// Approve a pending knock: pair its fingerprint (under `name_override` if the operator
+    /// labeled it, else the knock's own name) and drop it from the queue. `Ok(None)` = no such
+    /// (or expired) id.
+    pub fn approve_pending(
+        &self,
+        id: u32,
+        name_override: Option<&str>,
+    ) -> Result<Option<PairedClient>> {
+        let entry = {
+            let mut pending = self.pending.lock().unwrap();
+            Self::expire_pending(&mut pending);
+            let Some(at) = pending.items.iter().position(|p| p.id == id) else {
+                return Ok(None);
+            };
+            pending.items.remove(at)
+        }; // pending lock released — add() takes the paired lock
+        let name = name_override.unwrap_or(&entry.name);
+        self.add(name, &entry.fp_hex)?;
+        Ok(Some(PairedClient {
+            name: name.to_string(),
+            fingerprint: entry.fp_hex,
+        }))
+    }
+
+    /// Deny (drop) a pending knock. Returns whether one was removed. The device's next knock
+    /// re-creates an entry — deny is "not now", not a blocklist.
+    pub fn deny_pending(&self, id: u32) -> bool {
+        let mut pending = self.pending.lock().unwrap();
+        let before = pending.items.len();
+        pending.items.retain(|p| p.id != id);
+        pending.items.len() != before
+    }
 }
 
 #[cfg(test)]
@@ -250,6 +451,101 @@ mod tests {
         let _ = std::fs::remove_file(&p);
     }
 
+    #[test]
+    fn pending_knock_approve_and_deny() {
+        let p = temp();
+        let _ = std::fs::remove_file(&p);
+        let np = NativePairing::load_with(Some(p.clone()), None, false).unwrap();
+        assert!(np.pending().is_empty());
+
+        // A knock appears; a re-knock from the same fingerprint refreshes (same id, new name)
+        // instead of duplicating.
+        np.note_pending("device aa11", "AA11");
+        np.note_pending("Bedroom TV", "aa11");
+        let pend = np.pending();
+        assert_eq!(pend.len(), 1, "re-knock dedups by fingerprint");
+        assert_eq!(pend[0].name, "Bedroom TV");
+        let id = pend[0].id;
+
+        // Deny drops it without pairing; the next knock gets a fresh id.
+        assert!(np.deny_pending(id));
+        assert!(!np.deny_pending(id));
+        assert!(np.pending().is_empty());
+        assert!(!np.is_paired("aa11"));
+
+        // Approve pairs the fingerprint (operator label wins) and clears the entry.
+        np.note_pending("device bb22", "BB22");
+        let id = np.pending()[0].id;
+        assert!(
+            np.approve_pending(9999, None).unwrap().is_none(),
+            "unknown id"
+        );
+        let client = np
+            .approve_pending(id, Some("Living Room"))
+            .unwrap()
+            .unwrap();
+        assert_eq!(client.name, "Living Room");
+        assert!(np.is_paired("bb22"), "approval pins the fingerprint");
+        assert!(np.pending().is_empty());
+        assert_eq!(np.list()[0].name, "Living Room");
+
+        // The cap evicts the oldest knock.
+        for i in 0..(PENDING_CAP + 3) {
+            np.note_pending("flood", &format!("f{i:03}"));
+        }
+        let pend = np.pending();
+        assert_eq!(pend.len(), PENDING_CAP);
+        assert_eq!(pend[0].fingerprint, "f003", "oldest entries evicted first");
+        let _ = std::fs::remove_file(&p);
+    }
+
+    #[test]
+    fn sanitize_strips_control_and_bidi() {
+        // ANSI escape + newline + a bidi override that could spoof the displayed name.
+        let dirty = "\u{1b}]0;evil\u{07}Good\nDevice\u{202E}xfp";
+        let clean = sanitize_device_name(dirty, "deadbeef00");
+        assert!(!clean.contains('\u{1b}') && !clean.contains('\n') && !clean.contains('\u{202E}'));
+        // ESC dropped (']' survives), BEL dropped, '\n'→space (Good Device), RLO dropped (no space).
+        assert_eq!(clean, "]0;evilGood Devicexfp");
+        // All-control / empty → fingerprint-derived fallback.
+        assert_eq!(
+            sanitize_device_name("\u{1b}\u{07}", "deadbeef00"),
+            "device deadbeef"
+        );
+        assert_eq!(sanitize_device_name("   ", "abc"), "device abc");
+        // Over-long names cap at a char boundary.
+        assert!(sanitize_device_name(&"x".repeat(200), "ab").len() <= 64);
+    }
+
+    #[test]
+    fn pairing_clears_a_pending_knock() {
+        let p = temp();
+        let _ = std::fs::remove_file(&p);
+        let np = NativePairing::load_with(Some(p.clone()), None, false).unwrap();
+        np.note_pending("Knocker", "cc44");
+        assert_eq!(np.pending().len(), 1);
+        // Pairing the same fingerprint (e.g. via the PIN ceremony) drops the stale pending entry.
+        np.add("Knocker", "CC44").unwrap();
+        assert!(
+            np.pending().is_empty(),
+            "a now-paired device must leave the approval list"
+        );
+        assert!(np.is_paired("cc44"));
+        let _ = std::fs::remove_file(&p);
+    }
+
+    #[test]
+    fn add_replaces_case_insensitively() {
+        let p = temp();
+        let _ = std::fs::remove_file(&p);
+        let np = NativePairing::load_with(Some(p.clone()), None, false).unwrap();
+        np.add("First", "AB12").unwrap();
+        np.add("Second", "ab12").unwrap(); // same device, different hex case
+        assert_eq!(np.list().len(), 1, "re-add must replace, not duplicate");
+        assert_eq!(np.list()[0].name, "Second");
+        let _ = std::fs::remove_file(&p);
+    }
+
     #[test]
     fn cli_flag_arms_with_no_expiry() {
         let p = temp();