merge discovery: DNS-SD walker + public peers endpoint

pyproject.toml

@@ -23,6 +23,7 @@ dependencies = [
     "pyotp>=2.9",
     "qrcode[pil]>=7.4",
     "itsdangerous>=2.1",
+    "dnspython>=2.4",
 ]
 
 [project.optional-dependencies]

src/psyc/_federation_cli.py

@@ -7,14 +7,14 @@ from __future__ import annotations
 
 import json
 from pathlib import Path
-from typing import Optional
+from typing import List, Optional
 
 import httpx
 import typer
 
 from psyc import db, log
-from psyc.lines import federation
-from psyc.result import Err
+from psyc.lines import discovery, federation, pulse
+from psyc.result import Err, Ok
 
 
 _log = log.get(__name__)
@@ -133,3 +133,80 @@ def register(typer_app: typer.Typer) -> None:
         db.init_db()
         federation.remove_peer(domain)
         typer.echo(f"removed {domain}")
+
+    # ---------- discovery (DNS-SD walker) ----------------------------------
+
+    @typer_app.command("fed-resolve")
+    def fed_resolve(
+        domain: str = typer.Argument(..., help="domain to look up via _psyc._tcp.<domain>"),
+        timeout: float = typer.Option(5.0, "--timeout", help="DNS lookup timeout, seconds"),
+    ) -> None:
+        """Resolve a domain's psyc DNS-SD record. Prints fingerprint + port."""
+        result = discovery.resolve_psyc(domain, timeout=timeout)
+        if isinstance(result, Err):
+            typer.echo(f"error: {result.reason}", err=True)
+            raise typer.Exit(1)
+        c = result.value
+        typer.echo(f"  domain      {c.domain}")
+        typer.echo(f"  fingerprint {c.fingerprint}")
+        typer.echo(f"  port        {c.port}")
+        typer.echo(f"  source      {c.source}")
+
+    @typer_app.command("fed-walk")
+    def fed_walk(
+        seeds: List[str] = typer.Argument(..., help="one or more seed domains"),
+        depth: int = typer.Option(2, "--depth", help="max BFS depth"),
+        max_peers: int = typer.Option(200, "--max-peers", help="cap discovered candidates"),
+        record: bool = typer.Option(False, "--record", help="persist candidates as status=unknown"),
+    ) -> None:
+        """Walk DNS-SD + peer-public from `seeds`. Prints discovered table."""
+        db.init_db()
+        cands = discovery.walk(seeds, max_depth=depth, max_peers=max_peers)
+        if not cands:
+            typer.echo("(no candidates discovered)")
+            return
+        typer.echo(f"{'domain':<32} {'fingerprint':<24} {'port':>5}  source")
+        for c in cands:
+            fp = f"{c.fingerprint[:8]}…{c.fingerprint[-8:]}"
+            typer.echo(f"{c.domain:<32} {fp:<24} {c.port:>5}  {c.source}")
+        if record:
+            for c in cands:
+                discovery.record_candidate(c)
+            typer.echo(f"recorded {len(cands)} candidate(s) into peers table")
+
+    @typer_app.command("fed-seeds-list")
+    def fed_seeds_list() -> None:
+        """Print the operator-curated discovery seed list."""
+        db.init_db()
+        seeds = pulse.get_discovery_seeds()
+        if not seeds:
+            typer.echo("(no seeds configured)")
+            return
+        for s in seeds:
+            typer.echo(s)
+
+    @typer_app.command("fed-seeds-add")
+    def fed_seeds_add(domain: str = typer.Argument(...)) -> None:
+        """Append a seed domain (no-op if already present)."""
+        db.init_db()
+        seeds = pulse.get_discovery_seeds()
+        d = domain.strip()
+        if d in seeds:
+            typer.echo(f"{d} already a seed")
+            return
+        seeds.append(d)
+        pulse.set_discovery_seeds(seeds)
+        typer.echo(f"added seed {d}")
+
+    @typer_app.command("fed-seeds-remove")
+    def fed_seeds_remove(domain: str = typer.Argument(...)) -> None:
+        """Remove a seed domain (no-op if absent)."""
+        db.init_db()
+        seeds = pulse.get_discovery_seeds()
+        d = domain.strip()
+        if d not in seeds:
+            typer.echo(f"{d} not in seeds")
+            return
+        seeds = [s for s in seeds if s != d]
+        pulse.set_discovery_seeds(seeds)
+        typer.echo(f"removed seed {d}")

src/psyc/cockpit/federation_routes.py

@@ -15,7 +15,7 @@ from fastapi.responses import HTMLResponse, JSONResponse, PlainTextResponse, Red
 from fastapi.templating import Jinja2Templates
 
 from psyc import db, log
-from psyc.lines import federation
+from psyc.lines import discovery, federation, pulse
 
 
 _log = log.get(__name__)
@@ -25,6 +25,10 @@ _log = log.get(__name__)
 _FEED_CACHE: Dict[str, Any] = {"ts": 0.0, "payload": None}
 _FEED_TTL = 60.0
 
+# Mirror the feed cache for the public peers list — same poll-load pattern.
+_PUBLIC_PEERS_CACHE: Dict[str, Any] = {"ts": 0.0, "payload": None}
+_PUBLIC_PEERS_TTL = 60.0
+
 
 def _admin_ok(request: Request) -> bool:
     return bool(request.session.get("admin_ok"))
@@ -38,6 +42,14 @@ def _cached_feed() -> Dict[str, Any]:
     return _FEED_CACHE["payload"]
 
 
+def _cached_public_peers() -> Any:
+    now = time.time()
+    if _PUBLIC_PEERS_CACHE["payload"] is None or (now - _PUBLIC_PEERS_CACHE["ts"]) > _PUBLIC_PEERS_TTL:
+        _PUBLIC_PEERS_CACHE["payload"] = discovery.public_peer_attestation()
+        _PUBLIC_PEERS_CACHE["ts"] = now
+    return _PUBLIC_PEERS_CACHE["payload"]
+
+
 def register(app: FastAPI, TEMPLATES: Jinja2Templates) -> None:
     """Mount all federation routes onto `app`."""
 
@@ -103,6 +115,54 @@ def register(app: FastAPI, TEMPLATES: Jinja2Templates) -> None:
         federation.remove_peer(domain)
         return RedirectResponse("/admin/federation", status_code=303)
 
+    # ---------- discovery (DNS-SD walker) ----------------------------
+
+    @app.get("/admin/federation/discovery", response_class=HTMLResponse)
+    def admin_discovery(request: Request) -> HTMLResponse:
+        if not _admin_ok(request):
+            return RedirectResponse("/admin", status_code=303)
+        seeds = pulse.get_discovery_seeds()
+        candidates = federation.list_peers()
+        flash = request.query_params.get("flash") or ""
+        return TEMPLATES.TemplateResponse(
+            request,
+            "admin_discovery.html",
+            {
+                "seeds": seeds,
+                "seeds_text": "\n".join(seeds),
+                "candidates": candidates,
+                "flash": flash,
+            },
+        )
+
+    @app.post("/admin/federation/discovery/seeds")
+    def admin_discovery_seeds(
+        request: Request,
+        seeds: str = Form(""),
+    ) -> RedirectResponse:
+        if not _admin_ok(request):
+            raise HTTPException(status_code=403, detail="admin session required")
+        lines = [line for line in seeds.splitlines()]
+        pulse.set_discovery_seeds(lines)
+        return RedirectResponse("/admin/federation/discovery?flash=seeds+saved", status_code=303)
+
+    @app.post("/admin/federation/discovery/walk")
+    def admin_discovery_walk(request: Request) -> RedirectResponse:
+        if not _admin_ok(request):
+            raise HTTPException(status_code=403, detail="admin session required")
+        seeds = pulse.get_discovery_seeds()
+        if not seeds:
+            return RedirectResponse("/admin/federation/discovery?flash=no+seeds+configured", status_code=303)
+        try:
+            cands = discovery.walk(seeds)
+            for c in cands:
+                discovery.record_candidate(c)
+            msg = f"discovered+{len(cands)}+candidates+from+{len(seeds)}+seed(s)"
+        except Exception as exc:  # noqa: BLE001 — surface the error to the operator
+            _log.warning("federation.discovery.walk.error", error=str(exc))
+            msg = f"walk+failed:+{str(exc)[:80]}"
+        return RedirectResponse(f"/admin/federation/discovery?flash={msg}", status_code=303)
+
     # ---------- public endpoints --------------------------------------
 
     @app.get("/federation/info")
@@ -122,4 +182,13 @@ def register(app: FastAPI, TEMPLATES: Jinja2Templates) -> None:
     def federation_feed() -> JSONResponse:
         return JSONResponse(_cached_feed())
 
+    @app.get("/federation/peers/public")
+    def federation_peers_public() -> JSONResponse:
+        """Publicly attested peer list — what other psyc walkers discover us through.
+
+        Only trusted peers leak; unknown + blocked are internal state and must
+        never appear here.
+        """
+        return JSONResponse(_cached_public_peers())
+
     _log.info("federation.routes.registered")

src/psyc/cockpit/templates/admin_discovery.html

@@ -0,0 +1,72 @@
+{% extends "base.html" %}
+{% block title %}Discovery — psyc admin{% endblock %}
+{% block content %}
+
+<section class="panel">
+  <div class="panel-head">
+    <h1>Peer discovery</h1>
+    <span class="count">{{ candidates|length }} candidate{{ '' if candidates|length == 1 else 's' }}</span>
+  </div>
+  <p class="page-intro">Walk DNS-SD records from a seed domain you know runs psyc, then recurse through its public peer list. Newly-found peers land here with status <code>unknown</code> — vouching is what eventually promotes them. Once seeds exist, enabling the <code>peer-pull</code> pulse pipeline runs this on a cadence.</p>
+  <p class="back"><a href="/admin/federation">← back to federation</a></p>
+
+  {% if flash %}
+  <div class="verdict verdict-clean">{{ flash }}</div>
+  {% endif %}
+</section>
+
+<section class="panel">
+  <div class="panel-head">
+    <h2>Seed domains</h2>
+    <span class="count">{{ seeds|length }} configured</span>
+  </div>
+  <p class="page-intro">One domain per line. Each seed is resolved via <code>_psyc._tcp.&lt;domain&gt;</code> SRV+TXT; its <code>/federation/peers/public</code> is fetched and recursed.</p>
+  <form method="post" action="/admin/federation/discovery/seeds" style="display:grid; gap:10px; max-width:680px;">
+    <textarea name="seeds" rows="6" class="lookup-input" style="font-family:ui-monospace,SFMono-Regular,Menlo,monospace; font-size:12px;" placeholder="peer1.example.com&#10;peer2.example.org">{{ seeds_text }}</textarea>
+    <div style="display:flex; gap:10px;">
+      <button type="submit" class="btn btn-enforce">save seeds</button>
+    </div>
+  </form>
+
+  <form method="post" action="/admin/federation/discovery/walk" style="margin-top:14px;">
+    <button type="submit" class="btn btn-approve" {% if not seeds %}disabled{% endif %}>walk now</button>
+  </form>
+</section>
+
+<section class="panel">
+  <div class="panel-head">
+    <h2>Recent candidates</h2>
+    <span class="count">{{ candidates|length }} in registry</span>
+  </div>
+  <p class="page-intro">Every peer the walker has ever found, newest first. Trusted/blocked statuses are preserved across re-walks — discovery never demotes a peer the operator has classified.</p>
+
+  {% if candidates %}
+  <table class="ledger">
+    <thead><tr><th>Domain</th><th>Fingerprint</th><th>Status</th><th>Discovered</th><th>Last seen</th><th>Notes</th></tr></thead>
+    <tbody>
+    {% for p in candidates %}
+      <tr class="ledger-row">
+        <td><strong>{{ p.domain }}</strong></td>
+        <td class="lg-sub" style="font-family:ui-monospace,SFMono-Regular,Menlo,monospace;">{{ p.fingerprint[:8] }}…{{ p.fingerprint[-8:] }}</td>
+        <td>
+          {% if p.status == 'trusted' %}
+            <span class="sev-badge" style="background:rgba(74,222,128,0.10); color:var(--green); border-color:var(--green);">trusted</span>
+          {% elif p.status == 'blocked' %}
+            <span class="sev-badge" style="background:rgba(248,113,113,0.10); color:var(--red); border-color:var(--red);">blocked</span>
+          {% else %}
+            <span class="sev-badge">{{ p.status }}</span>
+          {% endif %}
+        </td>
+        <td class="lg-ts">{{ (p.discovered_at or '')[:16] | replace('T', ' ') }}</td>
+        <td class="lg-ts">{{ ((p.last_seen or '')[:16] | replace('T', ' ')) or '—' }}</td>
+        <td class="lg-sub">{{ (p.notes or '')[:60] }}</td>
+      </tr>
+    {% endfor %}
+    </tbody>
+  </table>
+  {% else %}
+  <p class="page-intro">(no candidates yet — add a seed above and walk)</p>
+  {% endif %}
+</section>
+
+{% endblock %}

src/psyc/db.py

@@ -313,6 +313,25 @@ def kill_switch_set(armed: bool, db_path: Path = DB_PATH) -> None:
         conn.execute(stmt)
 
 
+def pulse_setting_get(key: str, db_path: Path = DB_PATH) -> Optional[str]:
+    """Fetch one row from pulse_settings by key; returns None if absent."""
+    stmt = select(pulse_settings.c.value).where(pulse_settings.c.key == key)
+    with engine(db_path).connect() as conn:
+        row = conn.execute(stmt).fetchone()
+    return str(row.value) if row else None
+
+
+def pulse_setting_set(key: str, value: str, db_path: Path = DB_PATH) -> None:
+    """Upsert one (key, value) into pulse_settings."""
+    stmt = sqlite_insert(pulse_settings).values(key=key, value=value)
+    stmt = stmt.on_conflict_do_update(
+        index_elements=[pulse_settings.c.key],
+        set_=dict(value=stmt.excluded.value),
+    )
+    with engine(db_path).begin() as conn:
+        conn.execute(stmt)
+
+
 # ---------- federation: peers + signal buffer ----------------------------
 
 def upsert_peer(row: dict, db_path: Path = DB_PATH) -> None:

src/psyc/lines/discovery.py

@@ -0,0 +1,357 @@
+"""Discovery — DNS-SD resolver + BFS peer-walker for internet-wide federation.
+
+Federation identity (psyc.lines.federation) gives every node a stable Ed25519
+keypair, a 32-hex fingerprint, and a DNS record format. This module is the
+*finder*: given a seed domain you suspect runs psyc, walk its DNS-SD records
+to learn the fingerprint, fetch its public peer list, and recurse.
+
+Newly-discovered peers always enter the `peers` table with status="unknown" —
+they do NOT become trusted by being seen; vouching is a separate concern
+(sibling module). Discovery only populates the candidate set.
+"""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from typing import Any, Dict, List, Optional, Set, Tuple
+
+import dns.exception
+import dns.rdatatype
+import dns.resolver
+import httpx
+from pydantic import BaseModel, Field
+
+from psyc import db, log
+from psyc.lines import federation
+from psyc.result import Err, Ok, Result
+
+
+_log = log.get(__name__)
+
+DEFAULT_TIMEOUT = 5.0
+DEFAULT_PORT = 443
+DEFAULT_MAX_DEPTH = 2
+DEFAULT_MAX_PEERS = 200
+
+_VALID_STATUSES = {"unknown", "trusted", "blocked", "vouched"}
+
+
+# ---------- candidate model --------------------------------------------------
+
+class PeerCandidate(BaseModel):
+    """A peer found by the resolver/walker — not yet vetted, just observed."""
+    domain: str
+    fingerprint: str
+    port: int = DEFAULT_PORT
+    source: str  # "dns-sd" | "peer-walk:<source-domain>"
+    discovered_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+
+
+# ---------- DNS-SD resolver --------------------------------------------------
+
+def _parse_txt_value(txt: str) -> Result[Dict[str, str], str]:
+    """Parse `v=psyc1 fp=<hex> alg=ed25519 path=...` → dict. Tolerant of order."""
+    out: Dict[str, str] = {}
+    for token in txt.strip().split():
+        if "=" not in token:
+            return Err(f"malformed TXT token (no '='): {token!r}")
+        k, v = token.split("=", 1)
+        out[k.strip()] = v.strip()
+    if out.get("v") != federation.FEED_VERSION:
+        return Err(f"unsupported version: {out.get('v')!r}")
+    fp = out.get("fp", "")
+    if len(fp) != 32 or any(c not in "0123456789abcdef" for c in fp.lower()):
+        return Err(f"bad fingerprint: {fp!r}")
+    if out.get("alg") and out["alg"] != federation.FEED_ALG:
+        return Err(f"unsupported alg: {out.get('alg')!r}")
+    return Ok(out)
+
+
+def _flatten_txt(rdata: Any) -> str:
+    """DNS TXT records are a sequence of byte-strings — join them. Tolerant of mocks."""
+    strings = getattr(rdata, "strings", None)
+    if strings is None:
+        return str(rdata).strip('"')
+    parts: List[str] = []
+    for s in strings:
+        if isinstance(s, bytes):
+            parts.append(s.decode("utf-8", errors="replace"))
+        else:
+            parts.append(str(s))
+    return "".join(parts)
+
+
+def resolve_psyc(domain: str, timeout: float = DEFAULT_TIMEOUT) -> Result[PeerCandidate, str]:
+    """Look up `_psyc._tcp.<domain>` SRV + TXT → return a candidate.
+
+    SRV gives target+port; TXT carries `v=psyc1 fp=... alg=ed25519 path=...`.
+    Any DNS failure, parse failure, or missing record returns Err.
+    """
+    name = f"_psyc._tcp.{domain}"
+    resolver = dns.resolver.Resolver()
+    resolver.lifetime = timeout
+    resolver.timeout = timeout
+
+    # SRV: target host + port.
+    port = DEFAULT_PORT
+    try:
+        srv_answers = resolver.resolve(name, "SRV")
+    except dns.resolver.NXDOMAIN:
+        return Err(f"no SRV record at {name} (NXDOMAIN)")
+    except dns.resolver.NoAnswer:
+        return Err(f"no SRV record at {name} (NoAnswer)")
+    except dns.exception.Timeout:
+        return Err(f"SRV lookup timed out for {name}")
+    except dns.exception.DNSException as exc:
+        return Err(f"SRV lookup failed for {name}: {exc}")
+    srv_list = list(srv_answers)
+    if not srv_list:
+        return Err(f"no SRV record at {name} (empty)")
+    try:
+        port = int(srv_list[0].port)
+    except Exception:
+        port = DEFAULT_PORT
+
+    # TXT: fingerprint + protocol metadata.
+    try:
+        txt_answers = resolver.resolve(name, "TXT")
+    except dns.resolver.NXDOMAIN:
+        return Err(f"no TXT record at {name} (NXDOMAIN)")
+    except dns.resolver.NoAnswer:
+        return Err(f"no TXT record at {name} (NoAnswer)")
+    except dns.exception.Timeout:
+        return Err(f"TXT lookup timed out for {name}")
+    except dns.exception.DNSException as exc:
+        return Err(f"TXT lookup failed for {name}: {exc}")
+    txt_list = list(txt_answers)
+    if not txt_list:
+        return Err(f"no TXT record at {name} (empty)")
+
+    last_err: Optional[str] = None
+    for rdata in txt_list:
+        value = _flatten_txt(rdata)
+        parsed = _parse_txt_value(value)
+        if isinstance(parsed, Ok):
+            return Ok(PeerCandidate(
+                domain=domain,
+                fingerprint=parsed.value["fp"].lower(),
+                port=port,
+                source="dns-sd",
+            ))
+        last_err = parsed.reason
+    return Err(f"no usable psyc TXT record at {name}: {last_err}")
+
+
+# ---------- HTTP probes ------------------------------------------------------
+
+def _base_url(domain: str, port: int) -> str:
+    if port == 443:
+        return f"https://{domain}"
+    return f"https://{domain}:{port}"
+
+
+def fetch_peer_info(domain: str, port: int = DEFAULT_PORT, timeout: float = DEFAULT_TIMEOUT,
+                    expected_fingerprint: Optional[str] = None) -> Result[Dict[str, Any], str]:
+    """GET /federation/info on a peer. Cross-checks fingerprint if provided.
+
+    The cross-check defends against MITM-injected TXT records — DNS said one
+    fingerprint, the live node's HTTPS-served info MUST agree.
+    """
+    url = _base_url(domain, port) + "/federation/info"
+    try:
+        with httpx.Client(timeout=timeout) as client:
+            r = client.get(url)
+            r.raise_for_status()
+            data = r.json()
+    except httpx.HTTPStatusError as exc:
+        return Err(f"HTTP {exc.response.status_code} from {url}")
+    except httpx.RequestError as exc:
+        return Err(f"network error fetching {url}: {exc}")
+    except ValueError as exc:
+        return Err(f"non-JSON response from {url}: {exc}")
+    except Exception as exc:  # noqa: BLE001 — anything weird is a failure
+        return Err(f"fetch failed for {url}: {exc}")
+    if not isinstance(data, dict):
+        return Err(f"unexpected info shape from {url}: {type(data).__name__}")
+    declared = str(data.get("fingerprint", "")).lower()
+    if expected_fingerprint and declared != expected_fingerprint.lower():
+        return Err(
+            f"fingerprint mismatch for {domain}: DNS said {expected_fingerprint!r} "
+            f"but /federation/info said {declared!r}"
+        )
+    return Ok(data)
+
+
+def fetch_public_peers(domain: str, port: int = DEFAULT_PORT,
+                       timeout: float = DEFAULT_TIMEOUT) -> Result[List[Dict[str, Any]], str]:
+    """GET /federation/peers/public on a peer. Returns the list as-is for the walker to dedupe."""
+    url = _base_url(domain, port) + "/federation/peers/public"
+    try:
+        with httpx.Client(timeout=timeout) as client:
+            r = client.get(url)
+            r.raise_for_status()
+            data = r.json()
+    except httpx.HTTPStatusError as exc:
+        return Err(f"HTTP {exc.response.status_code} from {url}")
+    except httpx.RequestError as exc:
+        return Err(f"network error fetching {url}: {exc}")
+    except ValueError as exc:
+        return Err(f"non-JSON response from {url}: {exc}")
+    except Exception as exc:  # noqa: BLE001
+        return Err(f"fetch failed for {url}: {exc}")
+    if not isinstance(data, list):
+        return Err(f"unexpected peers shape from {url}: {type(data).__name__}")
+    out: List[Dict[str, Any]] = []
+    for item in data:
+        if isinstance(item, dict) and item.get("domain") and item.get("fingerprint"):
+            out.append(item)
+    return Ok(out)
+
+
+# ---------- BFS walker -------------------------------------------------------
+
+def walk(seeds: List[str], max_depth: int = DEFAULT_MAX_DEPTH,
+         max_peers: int = DEFAULT_MAX_PEERS, timeout: float = DEFAULT_TIMEOUT) -> List[PeerCandidate]:
+    """Breadth-first walk from `seeds` → discovered candidates.
+
+    For each domain: DNS-SD resolve → fetch /info to verify fingerprint →
+    fetch /peers/public → enqueue its domains for the next layer. Dedupes on
+    (domain, fingerprint). Skips our own fingerprint to avoid loops. All
+    errors are logged but non-fatal — one bad peer doesn't abort the walk.
+    """
+    own_fp = ""
+    try:
+        own_fp = federation.node_fingerprint()
+    except Exception as exc:  # noqa: BLE001 — discovery should work even pre-keygen
+        _log.info("discovery.walk.no_own_fp", error=str(exc))
+
+    seen_pairs: Set[Tuple[str, str]] = set()
+    seen_domains: Set[str] = set()
+    out: List[PeerCandidate] = []
+
+    # Queue of (domain, depth, source). Seeds enter at depth 0.
+    frontier: List[Tuple[str, int, str]] = [(d.strip(), 0, "dns-sd") for d in seeds if d and d.strip()]
+    next_layer: List[Tuple[str, int, str]] = []
+
+    while frontier:
+        domain, depth, source = frontier.pop(0)
+        if domain in seen_domains:
+            if not frontier:
+                frontier, next_layer = next_layer, []
+            continue
+        seen_domains.add(domain)
+        if len(out) >= max_peers:
+            _log.info("discovery.walk.cap.peers", cap=max_peers)
+            break
+
+        resolved = resolve_psyc(domain, timeout=timeout)
+        if isinstance(resolved, Err):
+            _log.info("discovery.resolve.skip", domain=domain, reason=resolved.reason)
+            if not frontier:
+                frontier, next_layer = next_layer, []
+            continue
+        cand = resolved.value
+        cand.source = source if depth > 0 else "dns-sd"
+
+        if cand.fingerprint == own_fp:
+            _log.info("discovery.skip.self", domain=domain)
+            if not frontier:
+                frontier, next_layer = next_layer, []
+            continue
+
+        pair = (cand.domain, cand.fingerprint)
+        if pair in seen_pairs:
+            if not frontier:
+                frontier, next_layer = next_layer, []
+            continue
+        seen_pairs.add(pair)
+
+        # Verify the live endpoint's fingerprint matches DNS. If we can't reach
+        # it, still record the DNS-discovered candidate — vouching can vet it
+        # later, and we don't want one HTTP outage to abort the walk.
+        info_res = fetch_peer_info(domain, port=cand.port, timeout=timeout,
+                                   expected_fingerprint=cand.fingerprint)
+        if isinstance(info_res, Err):
+            _log.info("discovery.info.skip", domain=domain, reason=info_res.reason)
+            out.append(cand)
+            if not frontier:
+                frontier, next_layer = next_layer, []
+            continue
+        out.append(cand)
+
+        # Recurse: fetch this peer's public-peers list, enqueue domains.
+        if depth + 1 <= max_depth:
+            peers_res = fetch_public_peers(domain, port=cand.port, timeout=timeout)
+            if isinstance(peers_res, Err):
+                _log.info("discovery.peers.skip", domain=domain, reason=peers_res.reason)
+            else:
+                for item in peers_res.value:
+                    child_domain = str(item.get("domain", "")).strip()
+                    if not child_domain or child_domain in seen_domains:
+                        continue
+                    child_source = f"peer-walk:{domain}"
+                    next_layer.append((child_domain, depth + 1, child_source))
+
+        if not frontier:
+            frontier, next_layer = next_layer, []
+
+    _log.info("discovery.walk.done", seeds=len(seeds), discovered=len(out), max_depth=max_depth)
+    return out
+
+
+# ---------- persistence ------------------------------------------------------
+
+def record_candidate(c: PeerCandidate, default_status: str = "unknown") -> None:
+    """Upsert a discovered candidate into the peers table.
+
+    Preserves any existing trusted/blocked status — discovery NEVER demotes a
+    peer the operator has already classified. Only updates last_seen.
+    """
+    if default_status not in _VALID_STATUSES:
+        default_status = "unknown"
+    existing = db.get_peer(c.domain)
+    now = c.discovered_at.isoformat()
+    if existing:
+        status = existing.get("status") or default_status
+        if status not in ("trusted", "blocked"):
+            status = default_status
+        db.upsert_peer(dict(
+            domain=c.domain,
+            fingerprint=existing.get("fingerprint") or c.fingerprint,
+            pubkey_pem=existing.get("pubkey_pem") or "",
+            status=status,
+            discovered_at=existing.get("discovered_at") or now,
+            last_seen=now,
+            notes=existing.get("notes"),
+        ))
+        return
+    db.upsert_peer(dict(
+        domain=c.domain,
+        fingerprint=c.fingerprint,
+        pubkey_pem="",  # populated when we successfully fetch /federation/key during vouching
+        status=default_status,
+        discovered_at=now,
+        last_seen=now,
+        notes=f"discovered via {c.source}",
+    ))
+    _log.info("discovery.recorded", domain=c.domain, fp=c.fingerprint, source=c.source)
+
+
+# ---------- public attestation -----------------------------------------------
+
+def public_peer_attestation() -> List[Dict[str, Any]]:
+    """List of peers we'll publicly attest to. Only `trusted` — never leaks unknown/blocked.
+
+    This is the surface that other psyc nodes' walkers read from us. We never
+    expose unknown or blocked peers — those are internal classification state.
+    """
+    out: List[Dict[str, Any]] = []
+    for row in db.list_peers():
+        if row.get("status") != "trusted":
+            continue
+        out.append({
+            "domain": row["domain"],
+            "fingerprint": row["fingerprint"],
+            "first_seen": row.get("discovered_at"),
+        })
+    return out

src/psyc/lines/pulse.py

@@ -134,8 +134,48 @@ def _run_respond_propose() -> str:
     return f"proposed {proposed} action(s) for {touched} case(s)"
 
 
+_DISCOVERY_SEEDS_KEY = "discovery_seeds"
+
+
+def get_discovery_seeds() -> List[str]:
+    """Operator-curated seed list for the discovery walker. Newline-separated in DB."""
+    raw = db.pulse_setting_get(_DISCOVERY_SEEDS_KEY)
+    if not raw:
+        return []
+    return [line.strip() for line in raw.splitlines() if line.strip()]
+
+
+def set_discovery_seeds(seeds: List[str]) -> None:
+    """Replace the seed list. Strips blanks + dedupes preserving order."""
+    seen: set = set()
+    cleaned: List[str] = []
+    for s in seeds:
+        v = (s or "").strip()
+        if not v or v in seen:
+            continue
+        seen.add(v)
+        cleaned.append(v)
+    db.pulse_setting_set(_DISCOVERY_SEEDS_KEY, "\n".join(cleaned))
+
+
 def _run_peer_pull() -> str:
-    return "federation not yet active"
+    """Walk DNS-SD + recurse over peer-public lists from the operator's seeds.
+
+    Records every fresh candidate into the `peers` table with status=unknown.
+    Vouching (sibling stage) is what eventually promotes them.
+    """
+    from psyc.lines import discovery
+
+    seeds = get_discovery_seeds()
+    if not seeds:
+        return "no seeds configured"
+    candidates = discovery.walk(seeds)
+    for c in candidates:
+        try:
+            discovery.record_candidate(c)
+        except Exception as exc:  # noqa: BLE001 — one bad write must not abort the batch
+            _log.warning("pulse.peer_pull.record.error", domain=c.domain, error=str(exc))
+    return f"discovered {len(candidates)} candidate(s) from {len(seeds)} seed(s)"
 
 
 def _run_vouch_refresh() -> str:

tests/test_discovery.py

@@ -0,0 +1,376 @@
+"""Discovery — DNS-SD parse + resolver, BFS walker, persistence, public endpoint."""
+
+from __future__ import annotations
+
+from typing import Any, Dict, List, Optional
+from unittest.mock import MagicMock, patch
+
+import dns.exception
+import dns.resolver
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from sqlalchemy import create_engine
+from starlette.middleware.sessions import SessionMiddleware
+
+from psyc import db
+from psyc.cockpit import federation_routes
+from psyc.lines import discovery, federation, pulse
+from psyc.lines.discovery import (
+    PeerCandidate,
+    _parse_txt_value,
+    fetch_peer_info,
+    fetch_public_peers,
+    public_peer_attestation,
+    record_candidate,
+    resolve_psyc,
+    walk,
+)
+from psyc.result import Err, Ok
+
+
+# ---------- fixtures ---------------------------------------------------------
+
+@pytest.fixture
+def fresh_db(tmp_path, monkeypatch):
+    test_db = tmp_path / "test.db"
+    eng = create_engine(f"sqlite:///{test_db}", future=True)
+    db._metadata.create_all(eng, checkfirst=True)
+    monkeypatch.setattr(db, "_engine", eng)
+    monkeypatch.setattr(db, "DB_PATH", test_db)
+    yield test_db
+
+
+@pytest.fixture
+def fed_dir(tmp_path, monkeypatch):
+    d = tmp_path / "federation"
+    monkeypatch.setattr(federation, "FED_DIR", d)
+    monkeypatch.setattr(federation, "PRIVATE_KEY_PATH", d / "node.key")
+    monkeypatch.setattr(federation, "PUBLIC_KEY_PATH", d / "node.pub")
+    yield d
+
+
+def _mk_srv(port: int = 443) -> Any:
+    rd = MagicMock()
+    rd.port = port
+    return rd
+
+
+def _mk_txt(value: str) -> Any:
+    rd = MagicMock()
+    rd.strings = [value.encode("utf-8")]
+    return rd
+
+
+# ---------- TXT parser -------------------------------------------------------
+
+def test_parse_txt_valid():
+    txt = "v=psyc1 fp=" + "a" * 32 + " alg=ed25519 path=/federation/feed"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Ok)
+    assert res.value["fp"] == "a" * 32
+    assert res.value["alg"] == "ed25519"
+
+
+def test_parse_txt_tolerates_token_order():
+    txt = "path=/federation/feed alg=ed25519 fp=" + "f" * 32 + " v=psyc1"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Ok)
+
+
+def test_parse_txt_rejects_wrong_version():
+    txt = "v=psyc2 fp=" + "a" * 32 + " alg=ed25519"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Err)
+    assert "version" in res.reason
+
+
+def test_parse_txt_rejects_bad_fingerprint_length():
+    txt = "v=psyc1 fp=deadbeef alg=ed25519"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Err)
+    assert "fingerprint" in res.reason
+
+
+def test_parse_txt_rejects_non_hex_fingerprint():
+    txt = "v=psyc1 fp=" + "z" * 32 + " alg=ed25519"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Err)
+
+
+def test_parse_txt_rejects_malformed_token():
+    txt = "v=psyc1 fp=" + "a" * 32 + " alg ed25519"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Err)
+    assert "malformed" in res.reason
+
+
+def test_parse_txt_rejects_wrong_alg():
+    txt = "v=psyc1 fp=" + "a" * 32 + " alg=rsa"
+    res = _parse_txt_value(txt)
+    assert isinstance(res, Err)
+
+
+# ---------- resolve_psyc -----------------------------------------------------
+
+def test_resolve_psyc_happy_path():
+    fp = "1" * 32
+    txt = f"v=psyc1 fp={fp} alg=ed25519 path=/federation/feed"
+
+    def fake_resolve(self, name, rdtype):
+        if rdtype == "SRV":
+            return [_mk_srv(port=8443)]
+        if rdtype == "TXT":
+            return [_mk_txt(txt)]
+        raise dns.exception.DNSException("unexpected")
+
+    with patch.object(dns.resolver.Resolver, "resolve", fake_resolve):
+        res = resolve_psyc("peer.example.com")
+    assert isinstance(res, Ok)
+    cand = res.value
+    assert cand.domain == "peer.example.com"
+    assert cand.fingerprint == fp
+    assert cand.port == 8443
+    assert cand.source == "dns-sd"
+
+
+def test_resolve_psyc_nxdomain_returns_err():
+    def fake_resolve(self, name, rdtype):
+        raise dns.resolver.NXDOMAIN()
+
+    with patch.object(dns.resolver.Resolver, "resolve", fake_resolve):
+        res = resolve_psyc("nothere.example")
+    assert isinstance(res, Err)
+    assert "NXDOMAIN" in res.reason
+
+
+def test_resolve_psyc_txt_malformed_returns_err():
+    def fake_resolve(self, name, rdtype):
+        if rdtype == "SRV":
+            return [_mk_srv()]
+        return [_mk_txt("v=psyc1 fp=garbage alg=ed25519")]
+
+    with patch.object(dns.resolver.Resolver, "resolve", fake_resolve):
+        res = resolve_psyc("peer.example")
+    assert isinstance(res, Err)
+    assert "TXT" in res.reason or "fingerprint" in res.reason
+
+
+def test_resolve_psyc_no_answer_returns_err():
+    def fake_resolve(self, name, rdtype):
+        raise dns.resolver.NoAnswer()
+
+    with patch.object(dns.resolver.Resolver, "resolve", fake_resolve):
+        res = resolve_psyc("peer.example")
+    assert isinstance(res, Err)
+    assert "NoAnswer" in res.reason
+
+
+# ---------- walk -------------------------------------------------------------
+
+def _stub_resolve(catalog: Dict[str, str]):
+    """Build a resolve_psyc stub that returns each domain's catalog fingerprint."""
+    def _stub(domain: str, timeout: float = 5.0):
+        if domain not in catalog:
+            return Err(f"no record for {domain}")
+        return Ok(PeerCandidate(
+            domain=domain,
+            fingerprint=catalog[domain],
+            port=443,
+            source="dns-sd",
+        ))
+    return _stub
+
+
+def _stub_fetch_info_ok(*args, **kwargs):
+    return Ok({"fingerprint": kwargs.get("expected_fingerprint", "")})
+
+
+def _stub_fetch_peers_factory(graph: Dict[str, List[Dict[str, str]]]):
+    def _stub(domain: str, port: int = 443, timeout: float = 5.0):
+        return Ok(graph.get(domain, []))
+    return _stub
+
+
+def test_walk_dedupes_by_fingerprint(fresh_db, fed_dir, monkeypatch):
+    # Two seeds, same fingerprint via different domains → only one survives the (domain,fp) dedupe
+    # but distinct domains both surface; the (domain, fp) pair just shouldn't repeat.
+    fp = "9" * 32
+    catalog = {"a.example": fp, "b.example": fp}
+    monkeypatch.setattr(discovery, "resolve_psyc", _stub_resolve(catalog))
+    monkeypatch.setattr(discovery, "fetch_peer_info", _stub_fetch_info_ok)
+    monkeypatch.setattr(discovery, "fetch_public_peers", _stub_fetch_peers_factory({}))
+    out = walk(["a.example", "b.example", "a.example"], max_depth=1)
+    # both unique domains made it in; the duplicate seed didn't re-enter
+    assert len(out) == 2
+    domains = {c.domain for c in out}
+    assert domains == {"a.example", "b.example"}
+
+
+def test_walk_respects_max_depth(fresh_db, fed_dir, monkeypatch):
+    catalog = {"d0.example": "0" * 32, "d1.example": "1" * 32, "d2.example": "2" * 32}
+    graph = {
+        "d0.example": [{"domain": "d1.example", "fingerprint": "1" * 32}],
+        "d1.example": [{"domain": "d2.example", "fingerprint": "2" * 32}],
+    }
+    monkeypatch.setattr(discovery, "resolve_psyc", _stub_resolve(catalog))
+    monkeypatch.setattr(discovery, "fetch_peer_info", _stub_fetch_info_ok)
+    monkeypatch.setattr(discovery, "fetch_public_peers", _stub_fetch_peers_factory(graph))
+    out = walk(["d0.example"], max_depth=1)
+    domains = {c.domain for c in out}
+    # depth 0: d0; depth 1: d1; depth 2 (d2) is excluded by max_depth=1
+    assert "d0.example" in domains and "d1.example" in domains
+    assert "d2.example" not in domains
+
+
+def test_walk_respects_max_peers(fresh_db, fed_dir, monkeypatch):
+    catalog = {f"d{i}.example": f"{i:032x}" for i in range(10)}
+    graph = {"d0.example": [{"domain": f"d{i}.example", "fingerprint": f"{i:032x}"} for i in range(1, 10)]}
+    monkeypatch.setattr(discovery, "resolve_psyc", _stub_resolve(catalog))
+    monkeypatch.setattr(discovery, "fetch_peer_info", _stub_fetch_info_ok)
+    monkeypatch.setattr(discovery, "fetch_public_peers", _stub_fetch_peers_factory(graph))
+    out = walk(["d0.example"], max_depth=2, max_peers=3)
+    assert len(out) <= 3
+
+
+def test_walk_skips_own_fingerprint(fresh_db, fed_dir, monkeypatch):
+    own = federation.node_fingerprint()
+    catalog = {"self.example": own, "peer.example": "f" * 32}
+    monkeypatch.setattr(discovery, "resolve_psyc", _stub_resolve(catalog))
+    monkeypatch.setattr(discovery, "fetch_peer_info", _stub_fetch_info_ok)
+    monkeypatch.setattr(discovery, "fetch_public_peers", _stub_fetch_peers_factory({}))
+    out = walk(["self.example", "peer.example"], max_depth=1)
+    domains = {c.domain for c in out}
+    assert "self.example" not in domains
+    assert "peer.example" in domains
+
+
+def test_walk_one_failure_does_not_abort(fresh_db, fed_dir, monkeypatch):
+    catalog = {"good.example": "a" * 32}  # bad.example is absent → Err on resolve
+    monkeypatch.setattr(discovery, "resolve_psyc", _stub_resolve(catalog))
+    monkeypatch.setattr(discovery, "fetch_peer_info", _stub_fetch_info_ok)
+    monkeypatch.setattr(discovery, "fetch_public_peers", _stub_fetch_peers_factory({}))
+    out = walk(["bad.example", "good.example"], max_depth=1)
+    assert len(out) == 1
+    assert out[0].domain == "good.example"
+
+
+# ---------- record_candidate -------------------------------------------------
+
+def test_record_candidate_inserts_as_unknown(fresh_db):
+    c = PeerCandidate(domain="new.example", fingerprint="a" * 32, source="dns-sd")
+    record_candidate(c)
+    row = db.get_peer("new.example")
+    assert row is not None
+    assert row["status"] == "unknown"
+    assert row["fingerprint"] == "a" * 32
+
+
+def test_record_candidate_preserves_trusted(fresh_db, fed_dir):
+    federation.register_peer("vip.example", "b" * 32, "PEM", status="trusted")
+    # walker re-discovers it
+    c = PeerCandidate(domain="vip.example", fingerprint="b" * 32, source="peer-walk:other.example")
+    record_candidate(c)
+    row = db.get_peer("vip.example")
+    assert row["status"] == "trusted"
+
+
+def test_record_candidate_preserves_blocked(fresh_db, fed_dir):
+    federation.register_peer("bad.example", "c" * 32, "PEM", status="blocked")
+    c = PeerCandidate(domain="bad.example", fingerprint="c" * 32, source="dns-sd")
+    record_candidate(c)
+    row = db.get_peer("bad.example")
+    assert row["status"] == "blocked"
+
+
+def test_record_candidate_updates_last_seen(fresh_db):
+    c = PeerCandidate(domain="repeat.example", fingerprint="d" * 32, source="dns-sd")
+    record_candidate(c)
+    first = db.get_peer("repeat.example")
+    # second pass — last_seen advances, discovered_at stays
+    c2 = PeerCandidate(domain="repeat.example", fingerprint="d" * 32, source="dns-sd")
+    record_candidate(c2)
+    second = db.get_peer("repeat.example")
+    assert second["discovered_at"] == first["discovered_at"]
+
+
+# ---------- public attestation -----------------------------------------------
+
+def test_public_peer_attestation_only_trusted(fresh_db, fed_dir):
+    federation.register_peer("trusted.example", "1" * 32, "PEM", status="trusted")
+    federation.register_peer("unknown.example", "2" * 32, "PEM", status="unknown")
+    federation.register_peer("blocked.example", "3" * 32, "PEM", status="blocked")
+    out = public_peer_attestation()
+    domains = {p["domain"] for p in out}
+    assert domains == {"trusted.example"}
+
+
+def test_public_peer_attestation_payload_shape(fresh_db, fed_dir):
+    federation.register_peer("t.example", "f" * 32, "PEM", status="trusted")
+    out = public_peer_attestation()
+    assert len(out) == 1
+    entry = out[0]
+    assert set(entry.keys()) == {"domain", "fingerprint", "first_seen"}
+
+
+# ---------- public endpoint via TestClient -----------------------------------
+
+def _mk_app() -> FastAPI:
+    app = FastAPI()
+    app.add_middleware(SessionMiddleware, secret_key="test-secret")
+    # Templates aren't exercised by the public endpoints we care about here.
+    from fastapi.templating import Jinja2Templates
+    import tempfile, os
+    tdir = tempfile.mkdtemp()
+    templates = Jinja2Templates(directory=tdir)
+    federation_routes.register(app, templates)
+    return app
+
+
+def test_public_peers_endpoint_excludes_unknown_blocked(fresh_db, fed_dir):
+    federation.register_peer("ok.example", "a" * 32, "PEM", status="trusted")
+    federation.register_peer("rude.example", "b" * 32, "PEM", status="blocked")
+    federation.register_peer("new.example", "c" * 32, "PEM", status="unknown")
+    # Flush in-memory cache from any earlier test.
+    federation_routes._PUBLIC_PEERS_CACHE["payload"] = None
+    federation_routes._PUBLIC_PEERS_CACHE["ts"] = 0.0
+    app = _mk_app()
+    client = TestClient(app)
+    r = client.get("/federation/peers/public")
+    assert r.status_code == 200
+    body = r.json()
+    domains = {p["domain"] for p in body}
+    assert "ok.example" in domains
+    assert "rude.example" not in domains
+    assert "new.example" not in domains
+
+
+# ---------- pulse integration ------------------------------------------------
+
+def test_discovery_seeds_roundtrip(fresh_db):
+    assert pulse.get_discovery_seeds() == []
+    pulse.set_discovery_seeds(["a.example", "b.example", "a.example", "", "  "])
+    # dedupe + strip blanks
+    assert pulse.get_discovery_seeds() == ["a.example", "b.example"]
+
+
+def test_peer_pull_pipeline_no_seeds(fresh_db, fed_dir, monkeypatch):
+    # peer-pull runner returns a clean message when nothing's configured.
+    outcome, result = pulse.run_now("peer-pull")
+    assert outcome == "ok"
+    assert "no seeds" in result
+
+
+def test_peer_pull_pipeline_with_seeds(fresh_db, fed_dir, monkeypatch):
+    pulse.set_discovery_seeds(["good.example"])
+    catalog = {"good.example": "e" * 32}
+    monkeypatch.setattr(discovery, "resolve_psyc", _stub_resolve(catalog))
+    monkeypatch.setattr(discovery, "fetch_peer_info", _stub_fetch_info_ok)
+    monkeypatch.setattr(discovery, "fetch_public_peers", _stub_fetch_peers_factory({}))
+    outcome, result = pulse.run_now("peer-pull")
+    assert outcome == "ok"
+    assert "discovered 1" in result
+    # And it was recorded.
+    row = db.get_peer("good.example")
+    assert row is not None
+    assert row["status"] == "unknown"