wire/

pair_invite.rs

//! Invite-URL pair flow (v0.4.0). Single-paste, zero-config pairing.
//!
//! Flow:
//!   A: `wire invite` → URL.
//!   A pastes URL into any channel (Discord, SMS, voice-read).
//!   B: `wire accept <URL>` → done. Both pinned.
//!
//! The invite URL is a self-contained bearer credential carrying A's signed
//! agent-card, relay coords, slot_token, and a single-use pair_nonce. B parses
//! it locally (no relay round-trip yet), pins A from the URL contents, then
//! POSTs a signed kind=1100 `pair_drop` event to A's slot using the slot_token
//! the URL granted. A's daemon (run_sync_pull) recognizes pair_drop events
//! that carry a matching pending_invite nonce, verifies the embedded card,
//! pins B, and consumes the nonce. Both sides paired.
//!
//! Trust model: pasting = trusting. Equivalent to Discord invite link, Zoom
//! join URL, Signal group invite. Operator's act of moving the URL between
//! channels IS the authentication ceremony. No SAS digits, no PAKE.
//!
//! The legacy SPAKE2 + SAS flow remains available via `wire pair --require-sas`
//! for operators who want the stronger MITM-resistance model.

use std::path::PathBuf;
use std::time::{SystemTime, UNIX_EPOCH};

use anyhow::{Context, Result, anyhow, bail};
use base64::Engine as _;
use base64::engine::general_purpose::URL_SAFE_NO_PAD as B64URL;
use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
use serde::{Deserialize, Serialize};
use serde_json::{Value, json};

use crate::config;

pub const DEFAULT_RELAY: &str = "https://wireup.net";
pub const DEFAULT_TTL_SECS: u64 = 86_400; // 24 hours

/// P0.2 (0.5.11): write a structured rejection record for `wire doctor`
/// to surface later. Best-effort — if we can't even open the file, fall
/// back to stderr so the operator at least sees the failure mode in their
/// shell. Anything is better than silent.
///
/// Lives at `$WIRE_HOME/state/wire/pair-rejected.jsonl`. One JSON line per
/// rejected pair event. Append-only.
pub(crate) fn record_pair_rejection(peer_handle: &str, code: &str, detail: &str) {
    let line = json!({
        "ts": std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|d| d.as_secs())
            .unwrap_or(0),
        "peer": peer_handle,
        "code": code,
        "detail": detail,
    });
    let serialised = match serde_json::to_string(&line) {
        Ok(s) => s,
        Err(e) => {
            eprintln!("wire: could not serialise pair-rejected entry: {e}");
            return;
        }
    };
    let path = match config::state_dir() {
        Ok(d) => d.join("pair-rejected.jsonl"),
        Err(e) => {
            eprintln!("wire: state_dir unresolved, dropping pair-rejected log: {e}");
            return;
        }
    };
    if let Some(parent) = path.parent() {
        if let Err(e) = std::fs::create_dir_all(parent) {
            eprintln!("wire: could not create {parent:?}: {e}");
            return;
        }
    }
    use std::io::Write;
    match std::fs::OpenOptions::new()
        .create(true)
        .append(true)
        .open(&path)
    {
        Ok(mut f) => {
            if let Err(e) = writeln!(f, "{serialised}") {
                eprintln!("wire: could not append pair-rejected to {path:?}: {e}");
            }
        }
        Err(e) => {
            eprintln!("wire: could not open {path:?}: {e}");
        }
    }
}

/// Decoded contents of an invite URL.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct InvitePayload {
    /// Schema version. Currently 1.
    pub v: u32,
    /// Issuer DID, e.g. `did:wire:paul`.
    pub did: String,
    /// Issuer's signed agent-card (full JSON).
    pub card: Value,
    /// Relay URL hosting the issuer's slot.
    pub relay_url: String,
    /// Issuer's slot id (32 hex chars).
    pub slot_id: String,
    /// Issuer's slot token (bearer auth for POSTing events to that slot).
    pub slot_token: String,
    /// Single-use nonce (32 random bytes hex).
    pub nonce: String,
    /// Unix timestamp after which this invite is invalid.
    pub exp: u64,
}

/// On-disk record for a minted invite, awaiting acceptance.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct PendingInvite {
    pub nonce: String,
    pub exp: u64,
    pub uses_remaining: u32,
    /// DIDs of peers who have already paired via this invite (for multi-use).
    pub accepted_by: Vec<String>,
    pub created_at: String,
}

/// Default-on policy: accept signed pair_drops from unknown peers (v0.5
/// zero-paste discovery). Operator can opt out by writing
/// `$WIRE_HOME/config/wire/policy.json` containing `{"accept_unknown_pair_drops": false}`.
fn open_mode_enabled() -> bool {
    let path = match config::config_dir() {
        Ok(p) => p.join("policy.json"),
        Err(_) => return true,
    };
    let bytes = match std::fs::read(&path) {
        Ok(b) => b,
        Err(_) => return true,
    };
    let v: Value = match serde_json::from_slice(&bytes) {
        Ok(v) => v,
        Err(_) => return true,
    };
    v.get("accept_unknown_pair_drops")
        .and_then(Value::as_bool)
        .unwrap_or(true)
}

pub fn pending_invites_dir() -> Result<PathBuf> {
    Ok(config::state_dir()?.join("pending-invites"))
}

fn now_unix() -> u64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0)
}

/// Hostname-derived default handle for auto-init. Falls back to "wire-user"
/// if hostname is unavailable. Sanitized to ASCII alphanumeric / '-' / '_'.
fn default_handle() -> String {
    let raw = hostname::get()
        .ok()
        .and_then(|s| s.into_string().ok())
        .unwrap_or_else(|| "wire-user".into());
    let sanitized: String = raw
        .chars()
        .map(|c| {
            if c.is_ascii_alphanumeric() || c == '-' || c == '_' {
                c
            } else {
                '-'
            }
        })
        .collect();
    if sanitized.is_empty() {
        "wire-user".into()
    } else {
        sanitized
    }
}

/// Ensure this node has an identity + relay slot. Idempotent.
/// Returns (did, relay_url, slot_id, slot_token).
pub fn ensure_self_with_relay(
    preferred_relay: Option<&str>,
) -> Result<(String, String, String, String)> {
    let relay = preferred_relay.unwrap_or(DEFAULT_RELAY);

    if !config::is_initialized()? {
        let handle = default_handle();
        crate::pair_session::init_self_idempotent(&handle, None, Some(relay))
            .with_context(|| format!("auto-init as did:wire:{handle}"))?;
    }

    let card = config::read_agent_card()?;
    let did = card
        .get("did")
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("agent-card missing did"))?
        .to_string();

    let mut relay_state = config::read_relay_state()?;
    let self_state = relay_state.get("self").cloned().unwrap_or(Value::Null);

    if self_state.is_null() || self_state.get("slot_id").and_then(Value::as_str).is_none() {
        let client = crate::relay_client::RelayClient::new(relay);
        client.check_healthz()?;
        let handle = crate::agent_card::display_handle_from_did(&did);
        let alloc = client.allocate_slot(Some(handle))?;
        relay_state["self"] = json!({
            "relay_url": relay,
            "slot_id": alloc.slot_id,
            "slot_token": alloc.slot_token,
        });
        config::write_relay_state(&relay_state)?;
    }

    let self_state = relay_state.get("self").cloned().unwrap_or(Value::Null);
    let relay_url = self_state["relay_url"].as_str().unwrap_or("").to_string();
    let slot_id = self_state["slot_id"].as_str().unwrap_or("").to_string();
    let slot_token = self_state["slot_token"].as_str().unwrap_or("").to_string();
    if relay_url.is_empty() || slot_id.is_empty() || slot_token.is_empty() {
        bail!("self relay state incomplete after auto-allocate");
    }
    Ok((did, relay_url, slot_id, slot_token))
}

/// Mint a fresh invite URL. Auto-inits + auto-allocates relay slot if needed.
pub fn mint_invite(
    ttl_secs: Option<u64>,
    uses: u32,
    preferred_relay: Option<&str>,
) -> Result<String> {
    let (did, relay_url, slot_id, slot_token) = ensure_self_with_relay(preferred_relay)?;

    let card = config::read_agent_card()?;
    let sk_seed = config::read_private_key()?;

    let mut nonce_bytes = [0u8; 32];
    use rand::RngCore;
    rand::thread_rng().fill_bytes(&mut nonce_bytes);
    let nonce = hex::encode(nonce_bytes);

    let ttl = ttl_secs.unwrap_or(DEFAULT_TTL_SECS);
    let exp = now_unix() + ttl;

    let payload = InvitePayload {
        v: 1,
        did: did.clone(),
        card,
        relay_url,
        slot_id,
        slot_token,
        nonce: nonce.clone(),
        exp,
    };
    let payload_bytes = serde_json::to_vec(&payload)?;

    let mut sk_arr = [0u8; 32];
    sk_arr.copy_from_slice(&sk_seed[..32]);
    let sk = SigningKey::from_bytes(&sk_arr);
    let sig = sk.sign(&payload_bytes);

    let token = format!(
        "{}.{}",
        B64URL.encode(&payload_bytes),
        B64URL.encode(sig.to_bytes())
    );
    let url = format!("wire://pair?v=1&inv={token}");

    let now = time::OffsetDateTime::now_utc()
        .format(&time::format_description::well_known::Rfc3339)
        .unwrap_or_default();
    let pending = PendingInvite {
        nonce: nonce.clone(),
        exp,
        uses_remaining: uses.max(1),
        accepted_by: vec![],
        created_at: now,
    };
    let dir = pending_invites_dir()?;
    std::fs::create_dir_all(&dir)?;
    let path = dir.join(format!("{nonce}.json"));
    std::fs::write(&path, serde_json::to_vec_pretty(&pending)?)?;

    Ok(url)
}

/// Parse an invite URL and verify the embedded signature against the embedded
/// card's first active verify key.
pub fn parse_invite(url: &str) -> Result<InvitePayload> {
    let rest = url
        .strip_prefix("wire://pair?")
        .ok_or_else(|| anyhow!("not a wire pair invite URL (must start with wire://pair?)"))?;
    let mut inv = None;
    for part in rest.split('&') {
        if let Some(v) = part.strip_prefix("inv=") {
            inv = Some(v);
        }
    }
    let token = inv.ok_or_else(|| anyhow!("invite URL missing `inv=` parameter"))?;
    let (payload_b64, sig_b64) = token
        .split_once('.')
        .ok_or_else(|| anyhow!("invite token missing `.` separator (payload.sig)"))?;
    let payload_bytes = B64URL
        .decode(payload_b64)
        .map_err(|e| anyhow!("invite payload b64 decode failed: {e}"))?;
    let sig_bytes = B64URL
        .decode(sig_b64)
        .map_err(|e| anyhow!("invite sig b64 decode failed: {e}"))?;

    let payload: InvitePayload = serde_json::from_slice(&payload_bytes)
        .map_err(|e| anyhow!("invite payload JSON decode failed: {e}"))?;

    if payload.v != 1 {
        bail!("invite schema version {} not supported", payload.v);
    }
    if now_unix() > payload.exp {
        bail!("invite expired (exp={}, now={})", payload.exp, now_unix());
    }

    // Verify the URL signature against the issuer's card key.
    crate::agent_card::verify_agent_card(&payload.card)
        .map_err(|e| anyhow!("invite issuer's card signature invalid: {e}"))?;

    let pk_b64 = payload
        .card
        .get("verify_keys")
        .and_then(Value::as_object)
        .and_then(|m| m.values().next())
        .and_then(|v| v.get("key"))
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("issuer card missing verify_keys[*].key"))?;
    let pk_bytes = crate::signing::b64decode(pk_b64)?;
    let mut pk_arr = [0u8; 32];
    if pk_bytes.len() != 32 {
        bail!("issuer pubkey wrong length");
    }
    pk_arr.copy_from_slice(&pk_bytes);
    let vk = VerifyingKey::from_bytes(&pk_arr)
        .map_err(|e| anyhow!("issuer pubkey decode failed: {e}"))?;
    let mut sig_arr = [0u8; 64];
    if sig_bytes.len() != 64 {
        bail!("invite sig wrong length");
    }
    sig_arr.copy_from_slice(&sig_bytes);
    let sig = Signature::from_bytes(&sig_arr);
    vk.verify(&payload_bytes, &sig)
        .map_err(|_| anyhow!("invite URL signature did not verify"))?;

    Ok(payload)
}

/// Accept an invite URL. Auto-inits + auto-allocates if needed. Pins issuer
/// from URL contents, then POSTs a signed pair_drop event to issuer's slot.
pub fn accept_invite(url: &str) -> Result<Value> {
    let payload = parse_invite(url)?;

    // Auto-init self on the issuer's relay (or env-default if reachable).
    let (our_did, our_relay, our_slot_id, our_slot_token) =
        ensure_self_with_relay(Some(&payload.relay_url))?;

    if our_did == payload.did {
        bail!("refusing to accept own invite (issuer DID matches self)");
    }

    // Pin issuer in trust + relay-state.
    let mut trust = config::read_trust()?;
    crate::trust::add_agent_card_pin(&mut trust, &payload.card, Some("VERIFIED"));
    config::write_trust(&trust)?;

    let peer_handle = crate::agent_card::display_handle_from_did(&payload.did).to_string();
    let mut relay_state = config::read_relay_state()?;
    relay_state["peers"][&peer_handle] = json!({
        "relay_url": payload.relay_url,
        "slot_id": payload.slot_id,
        "slot_token": payload.slot_token,
    });
    config::write_relay_state(&relay_state)?;

    // Build signed pair_drop event carrying our own card + slot coords +
    // the issuer's pair_nonce. Issuer's daemon will look it up against
    // pending-invites and complete the bilateral pin.
    let our_card = config::read_agent_card()?;
    let sk_seed = config::read_private_key()?;
    let our_handle = crate::agent_card::display_handle_from_did(&our_did).to_string();
    let pk_b64 = our_card
        .get("verify_keys")
        .and_then(Value::as_object)
        .and_then(|m| m.values().next())
        .and_then(|v| v.get("key"))
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("our agent-card missing verify_keys[*].key"))?;
    let pk_bytes = crate::signing::b64decode(pk_b64)?;

    let now = time::OffsetDateTime::now_utc()
        .format(&time::format_description::well_known::Rfc3339)
        .unwrap_or_default();
    let event = json!({
        "schema_version": crate::signing::EVENT_SCHEMA_VERSION,
        "timestamp": now,
        "from": our_did,
        "to": payload.did,
        "type": "pair_drop",
        "kind": 1100u32,
        "body": {
            "card": our_card,
            "relay_url": our_relay,
            "slot_id": our_slot_id,
            "slot_token": our_slot_token,
            "pair_nonce": payload.nonce,
        },
    });
    let signed = crate::signing::sign_message_v31(&event, &sk_seed, &pk_bytes, &our_handle)?;
    let event_id = signed["event_id"].as_str().unwrap_or("").to_string();

    let client = crate::relay_client::RelayClient::new(&payload.relay_url);
    client
        .post_event(&payload.slot_id, &payload.slot_token, &signed)
        .with_context(|| {
            format!(
                "POST pair_drop to {} slot {}",
                payload.relay_url, payload.slot_id
            )
        })?;

    Ok(json!({
        "paired_with": payload.did,
        "peer_handle": peer_handle,
        "event_id": event_id,
        "status": "drop_sent",
    }))
}

/// Consume a pair_drop event during daemon pull. Returns `Ok(Some(peer_did))`
/// if the event matched a pending invite and the peer was pinned. Returns
/// `Ok(None)` if not a pair_drop or no matching invite. Errors only on real
/// problems (bad sig over event, IO failure).
pub fn maybe_consume_pair_drop(event: &Value) -> Result<Option<String>> {
    let kind = event.get("kind").and_then(Value::as_u64).unwrap_or(0);
    let type_str = event.get("type").and_then(Value::as_str).unwrap_or("");
    if kind != 1100 || type_str != "pair_drop" {
        return Ok(None);
    }
    let body = match event.get("body") {
        Some(b) => b,
        None => return Ok(None),
    };

    // v0.5: accept handle-initiated pair_drops too (no pair_nonce). These
    // come via `wire add <handle>` → POST /v1/handle/intro. Anchored only
    // by the embedded signed card. Gated by config `accept_unknown_pair_drops`
    // (default true). For nonce-bearing drops the existing v0.4 invite-URL
    // path stays in force.
    let nonce_opt = body
        .get("pair_nonce")
        .and_then(Value::as_str)
        .map(str::to_string);
    let mut pending: Option<PendingInvite> = None;
    let mut invite_path: Option<std::path::PathBuf> = None;
    if let Some(nonce) = nonce_opt.as_deref() {
        let dir = pending_invites_dir()?;
        let path = dir.join(format!("{nonce}.json"));
        if path.exists() {
            let p: PendingInvite = serde_json::from_slice(&std::fs::read(&path)?)
                .with_context(|| format!("reading pending invite {path:?}"))?;
            if now_unix() > p.exp {
                // P0.2: warn if cleanup fails — orphaned expired invites in
                // `pending-invites/` will pile up and confuse `wire doctor`.
                if let Err(e) = std::fs::remove_file(&path) {
                    eprintln!(
                        "wire: could not delete expired invite {path:?}: {e}"
                    );
                }
                return Ok(None);
            }
            pending = Some(p);
            invite_path = Some(path);
        } else if !open_mode_enabled() {
            // Nonce present but unknown locally, and open mode disabled →
            // refuse silently (the event will fall through to the normal
            // verify path which won't trust the sender yet).
            return Ok(None);
        }
    } else if !open_mode_enabled() {
        // No nonce + open mode disabled → ignore. Operator must opt in to
        // be discoverable via zero-paste `wire add`.
        return Ok(None);
    }

    let peer_card = body
        .get("card")
        .cloned()
        .ok_or_else(|| anyhow!("pair_drop body missing card"))?;
    crate::agent_card::verify_agent_card(&peer_card)
        .map_err(|e| anyhow!("pair_drop peer card sig invalid: {e}"))?;

    let peer_did = peer_card
        .get("did")
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("peer card missing did"))?
        .to_string();
    let peer_handle = crate::agent_card::display_handle_from_did(&peer_did).to_string();

    // Verify the event signature now that we have peer's pubkey.
    let mut tmp_trust = config::read_trust()?;
    crate::trust::add_agent_card_pin(&mut tmp_trust, &peer_card, Some("VERIFIED"));
    crate::signing::verify_message_v31(event, &tmp_trust)
        .map_err(|e| anyhow!("pair_drop event sig verify failed: {e}"))?;

    // Pin peer in trust + relay-state.
    config::write_trust(&tmp_trust)?;
    let peer_relay = body.get("relay_url").and_then(Value::as_str).unwrap_or("");
    let peer_slot_id = body.get("slot_id").and_then(Value::as_str).unwrap_or("");
    let peer_slot_token = body.get("slot_token").and_then(Value::as_str).unwrap_or("");
    if peer_relay.is_empty() || peer_slot_id.is_empty() || peer_slot_token.is_empty() {
        bail!("pair_drop body missing relay_url/slot_id/slot_token");
    }
    let mut relay_state = config::read_relay_state()?;
    relay_state["peers"][&peer_handle] = json!({
        "relay_url": peer_relay,
        "slot_id": peer_slot_id,
        "slot_token": peer_slot_token,
    });
    config::write_relay_state(&relay_state)?;

    // Consume invite (single-use default; decrement uses for multi-use).
    // Skipped entirely for handle-initiated pair_drops (no pending record).
    if let (Some(pending), Some(invite_path)) = (pending, invite_path) {
        if pending.uses_remaining <= 1 {
            // P0.2: warn — leaking single-use invite files lets them get
            // accidentally re-consumed if the file timestamp parser glitches
            // or a backup tool reverts state. Not fatal but worth flagging.
            if let Err(e) = std::fs::remove_file(&invite_path) {
                eprintln!(
                    "wire: could not delete consumed invite {invite_path:?}: {e}"
                );
            }
        } else {
            let mut updated = pending.clone();
            updated.uses_remaining -= 1;
            updated.accepted_by.push(peer_did.clone());
            std::fs::write(&invite_path, serde_json::to_vec_pretty(&updated)?)?;
        }
    }

    crate::os_notify::toast(
        &format!("wire — paired with {peer_handle}"),
        "Invite accepted. Ready to send + receive.",
    );

    // v0.5: if this was a handle-initiated drop (no nonce), the sender doesn't
    // know OUR slot_token yet — they can post to our `/v1/handle/intro/<nick>`
    // but they can't `wire send` back through the normal slot endpoint until
    // they have it. Send a `pair_drop_ack` event back carrying our slot_token.
    //
    // P0.2 (0.5.11): NOT silent anymore. The bilateral pin only completes if
    // this POST succeeds — if we drop the error, the peer never gets our
    // slot_token and sits forever in PENDING_ACK from their side, with no
    // visible failure on either side. That was the 30-min-debug failure mode
    // earlier today. Log loudly + record to pair-rejected so `wire doctor`
    // can surface it.
    if nonce_opt.is_none() {
        if let Err(e) =
            send_pair_drop_ack(&peer_handle, peer_relay, peer_slot_id, peer_slot_token)
        {
            eprintln!(
                "wire: pair_drop_ack send to {peer_handle} @ {peer_relay} slot {peer_slot_id} FAILED: {e}. \
                 inbound pin succeeded but peer cannot bilateral-pin without our slot_token. \
                 retry with `wire add {peer_handle}@<their-relay>` or have peer re-add us."
            );
            record_pair_rejection(
                &peer_handle,
                "pair_drop_ack_send_failed",
                &e.to_string(),
            );
        }
    }

    Ok(Some(peer_did))
}

/// Send a `pair_drop_ack` event (kind=1101) carrying OUR slot_token to a peer
/// who just intro'd to us via `/v1/handle/intro/<nick>`. Completes the
/// zero-paste bidirectional pin. Best-effort: errors are logged but don't
/// propagate, since the inbound pair_drop pin already succeeded and the
/// operator can retry from either side.
fn send_pair_drop_ack(
    peer_handle: &str,
    peer_relay: &str,
    peer_slot_id: &str,
    peer_slot_token: &str,
) -> Result<()> {
    // Load our own card + relay coords.
    let our_card = config::read_agent_card()?;
    let our_did = our_card
        .get("did")
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("our card missing did"))?
        .to_string();
    let our_handle = crate::agent_card::display_handle_from_did(&our_did).to_string();
    let relay_state = config::read_relay_state()?;
    let self_state = relay_state.get("self").cloned().unwrap_or(Value::Null);
    let our_relay = self_state
        .get("relay_url")
        .and_then(Value::as_str)
        .unwrap_or("")
        .to_string();
    let our_slot_id = self_state
        .get("slot_id")
        .and_then(Value::as_str)
        .unwrap_or("")
        .to_string();
    let our_slot_token = self_state
        .get("slot_token")
        .and_then(Value::as_str)
        .unwrap_or("")
        .to_string();
    if our_relay.is_empty() || our_slot_id.is_empty() || our_slot_token.is_empty() {
        bail!("self relay state incomplete; cannot emit pair_drop_ack");
    }

    let sk_seed = config::read_private_key()?;
    let pk_b64 = our_card
        .get("verify_keys")
        .and_then(Value::as_object)
        .and_then(|m| m.values().next())
        .and_then(|v| v.get("key"))
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("our card missing verify_keys[*].key"))?;
    let pk_bytes = crate::signing::b64decode(pk_b64)?;

    let now = time::OffsetDateTime::now_utc()
        .format(&time::format_description::well_known::Rfc3339)
        .unwrap_or_default();
    let event = json!({
        "schema_version": crate::signing::EVENT_SCHEMA_VERSION,
        "timestamp": now,
        "from": our_did,
        "to": format!("did:wire:{peer_handle}"),
        "type": "pair_drop_ack",
        "kind": 1101u32,
        "body": {
            "relay_url": our_relay,
            "slot_id": our_slot_id,
            "slot_token": our_slot_token,
        },
    });
    let signed = crate::signing::sign_message_v31(&event, &sk_seed, &pk_bytes, &our_handle)?;
    let client = crate::relay_client::RelayClient::new(peer_relay);
    client
        .post_event(peer_slot_id, peer_slot_token, &signed)
        .with_context(|| format!("POST pair_drop_ack to {peer_relay} slot {peer_slot_id}"))?;
    Ok(())
}

/// Consume a `pair_drop_ack` event during daemon pull. Updates
/// relay-state.peers[<peer>] with the ack's slot_token so we can `wire send`
/// to the peer. Returns `Ok(true)` if applied. Idempotent.
pub fn maybe_consume_pair_drop_ack(event: &Value) -> Result<bool> {
    let kind = event.get("kind").and_then(Value::as_u64).unwrap_or(0);
    let type_str = event.get("type").and_then(Value::as_str).unwrap_or("");
    if kind != 1101 || type_str != "pair_drop_ack" {
        return Ok(false);
    }
    let body = match event.get("body") {
        Some(b) => b,
        None => return Ok(false),
    };
    let from = event
        .get("from")
        .and_then(Value::as_str)
        .ok_or_else(|| anyhow!("ack missing 'from'"))?;
    let peer_handle = crate::agent_card::display_handle_from_did(from).to_string();
    let peer_relay = body.get("relay_url").and_then(Value::as_str).unwrap_or("");
    let peer_slot_id = body.get("slot_id").and_then(Value::as_str).unwrap_or("");
    let peer_slot_token = body.get("slot_token").and_then(Value::as_str).unwrap_or("");
    if peer_relay.is_empty() || peer_slot_id.is_empty() || peer_slot_token.is_empty() {
        bail!("pair_drop_ack body missing relay_url/slot_id/slot_token");
    }
    let mut relay_state = config::read_relay_state()?;
    relay_state["peers"][&peer_handle] = json!({
        "relay_url": peer_relay,
        "slot_id": peer_slot_id,
        "slot_token": peer_slot_token,
    });
    config::write_relay_state(&relay_state)?;
    crate::os_notify::toast(
        &format!("wire — pair complete with {peer_handle}"),
        "Both sides bound. Ready to send + receive.",
    );
    Ok(true)
}

// Earlier note: "tests removed because of WIRE_HOME race." That's no longer
// true — `config::test_support::with_temp_home` serialises env-mutating
// tests behind a process-wide mutex, so unit tests here are safe again.
// Keep e2e coverage in `tests/e2e_invite_pair.rs` for full-flow paranoia.

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config;

    #[test]
    fn record_pair_rejection_writes_jsonl_under_state_dir() {
        // P0.2: silent fails must leave a trace. This is what `wire doctor`
        // (P1.6) will surface. If the file isn't written, `wire doctor`
        // can't see the problem — same silent-fail class we're fixing.
        config::test_support::with_temp_home(|| {
            super::record_pair_rejection(
                "slancha-spark",
                "pair_drop_ack_send_failed",
                "POST returned 502",
            );
            let path = config::state_dir().unwrap().join("pair-rejected.jsonl");
            assert!(
                path.exists(),
                "record_pair_rejection must create {path:?}"
            );
            let body = std::fs::read_to_string(&path).unwrap();
            let line = body.lines().last().expect("at least one line");
            let parsed: Value = serde_json::from_str(line).expect("valid JSON");
            assert_eq!(parsed["peer"], "slancha-spark");
            assert_eq!(parsed["code"], "pair_drop_ack_send_failed");
            assert_eq!(parsed["detail"], "POST returned 502");
            assert!(parsed["ts"].as_u64().unwrap_or(0) > 0);
        });
    }

    #[test]
    fn record_pair_rejection_appends_multiple_lines() {
        // Multiple silent fails in one session must each leave a record —
        // it's append-only, not a single most-recent slot.
        config::test_support::with_temp_home(|| {
            super::record_pair_rejection("a", "code_a", "detail_a");
            super::record_pair_rejection("b", "code_b", "detail_b");
            super::record_pair_rejection("c", "code_c", "detail_c");
            let path = config::state_dir().unwrap().join("pair-rejected.jsonl");
            let body = std::fs::read_to_string(&path).unwrap();
            let lines: Vec<&str> = body.lines().collect();
            assert_eq!(lines.len(), 3, "expected 3 entries, got {}", lines.len());
            for (i, peer) in ["a", "b", "c"].iter().enumerate() {
                let parsed: Value = serde_json::from_str(lines[i]).unwrap();
                assert_eq!(parsed["peer"], *peer);
            }
        });
    }
}