diff --git a/TODO.md b/TODO.md
index a84af5f5..a55d9170 100644
--- a/TODO.md
+++ b/TODO.md
@@ -27,19 +27,10 @@ Pick anything from here when relevant. Cross-cutting design notes live in
 
 ## UI / UX
 
-- **State badge: compacting + napping states.** Idle/thinking already
-  ship (driven from SSE turn_start/turn_end). Add `compacting 📦` and
-  `napping 😴` once the `/compact` trigger and `nap` tool exist —
-  both need a harness signal (an explicit `LiveEvent::StateChange`
-  variant or piggyback on Note).
-- **Server-side state badge.** Today the badge is computed client-side
-  from `turn_start`/`turn_end` events. On page reload mid-turn the
-  history replay re-derives it, but with a `compacting` / `napping`
-  state coming and a non-trivial state machine it's better to track
-  authoritative state in the harness and expose it via
-  `GET /api/state` (`status: "thinking" | "idle" | "compacting" |
-  "napping"`). JS just renders. Drops the
-  derive-from-events-and-pray code path.
+- **State badge: napping state.** Idle / thinking / compacting
+  already ship from server-side `TurnState`. Add `napping 😴`
+  once the `nap` tool exists — it just adds a new `TurnState`
+  variant the harness flips into for the duration of the nap.
 - **Terminal: `/model` slash command.** Operator-typeable model
   override from the terminal. Depends on the model-override work
   above; once an override mechanism exists, wire a `/model <name>`
@@ -107,17 +98,6 @@ Pick anything from here when relevant. Cross-cutting design notes live in
 
 ## Lifecycle / reliability
 
-- **journald viewer per container in the dashboard.** Surface the
-  equivalent of `journalctl -M h-coder -b` in the dashboard so the
-  operator can see container logs without ssh-ing in. Optional
-  filter by hive-specific systemd unit (`hive-ag3nt.service`,
-  `hive-m1nd.service`). Implementation: backend shells out to
-  `journalctl -M <container> -b --output=short-iso --no-pager`
-  (optionally `-u <unit>`), streams or paginates the result over a
-  new dashboard endpoint. Could be a `<details>` per container row
-  or a dedicated page. Honest journalctl, not the in-container
-  events stream — those are different surfaces (events = claude turn
-  loop; journalctl = systemd-wide logs incl. boot, network, etc.).
 - **Container crash events.** Watch `container@*.service` via D-Bus, push
   `HelperEvent::ContainerCrash` to the manager's inbox so the manager can
   react (restart, escalate, etc.).
diff --git a/hive-ag3nt/assets/agent.css b/hive-ag3nt/assets/agent.css
index 13031836..aeb165a6 100644
--- a/hive-ag3nt/assets/agent.css
+++ b/hive-ag3nt/assets/agent.css
@@ -228,6 +228,11 @@ pre.diff {
   text-shadow: 0 0 6px rgba(250, 179, 135, 0.65);
   animation: badge-pulse 1.8s ease-in-out infinite;
 }
+.state-badge.state-compacting {
+  color: var(--purple); border-color: var(--purple);
+  text-shadow: 0 0 6px rgba(203, 166, 247, 0.65);
+  animation: badge-pulse 1.8s ease-in-out infinite;
+}
 .state-badge.state-just-changed {
   animation: state-flash 600ms ease-out;
 }
diff --git a/hive-ag3nt/assets/app.js b/hive-ag3nt/assets/app.js
index 2702e7cc..1e506797 100644
--- a/hive-ag3nt/assets/app.js
+++ b/hive-ag3nt/assets/app.js
@@ -291,10 +291,11 @@
   // each second so the "· 12s" suffix stays current. State changes
   // trigger a short flash animation via .state-just-changed.
   const STATE_LABELS = {
-    loading:  { glyph: '…',  text: 'booting' },
-    offline:  { glyph: '○',  text: 'offline' },
-    idle:     { glyph: '💤', text: 'idle' },
-    thinking: { glyph: '🧠', text: 'thinking' },
+    loading:    { glyph: '…',  text: 'booting' },
+    offline:    { glyph: '○',  text: 'offline' },
+    idle:       { glyph: '💤', text: 'idle' },
+    thinking:   { glyph: '🧠', text: 'thinking' },
+    compacting: { glyph: '📦', text: 'compacting' },
   };
   let stateName = 'loading';
   let stateSince = Date.now();
@@ -318,19 +319,22 @@
     if (cancelBtn) cancelBtn.hidden = stateName !== 'thinking';
   }
   function setState(next) {
-    if (next === stateName) return;
-    // Capture the just-ending state's duration when leaving 'thinking'
-    // so the operator can eyeball turn length without scrolling the
-    // terminal back.
+    setStateAbs(next, Math.floor(Date.now() / 1000));
+  }
+  /// Set state with an authoritative since-unix from the server. Lets
+  /// `last turn` track the actual server-side duration rather than
+  /// whatever the client perceived between SSE events.
+  function setStateAbs(next, sinceUnix) {
+    if (next === stateName && sinceUnix * 1000 === stateSince) return;
     if (stateName === 'thinking' && next !== 'thinking') {
       const elapsedMs = Date.now() - stateSince;
       renderLastTurn(elapsedMs);
     }
+    const flashing = next !== stateName;
     stateName = next;
-    stateSince = Date.now();
+    stateSince = sinceUnix * 1000;
     const badge = $('state-badge');
-    if (badge) {
-      // Re-add the flash class so the animation replays.
+    if (badge && flashing) {
       badge.classList.remove('state-just-changed');
       void badge.offsetWidth;
       badge.classList.add('state-just-changed');
@@ -411,11 +415,15 @@
       if (!headerSet) { setHeader(s.label, s.dashboard_port); headerSet = true; }
       renderTermInput(s.label, s.status === 'online');
       renderInbox(s.inbox || []);
-      // Drive the state badge from the harness status. Live SSE events
-      // override to 'thinking' / 'idle' as turns start/end; this only
-      // kicks in for the not-online (offline) case and the initial seed.
-      if (s.status !== 'online') setState('offline');
-      else if (stateName === 'loading' || stateName === 'offline') setState('idle');
+      // Authoritative state comes from the harness via /api/state.
+      // Login-not-yet → 'offline'; otherwise use the server-reported
+      // turn_state (idle / thinking / compacting). stateSince in
+      // unix-seconds is converted to a client-side Date.now() anchor.
+      if (s.status !== 'online') {
+        setState('offline');
+      } else if (s.turn_state) {
+        setStateAbs(s.turn_state, s.turn_state_since);
+      }
       // Skip the re-render if nothing structurally changed. The most
       // common case is `online` polling itself — without this guard, the
       // operator's <input value> gets clobbered every cycle.
diff --git a/hive-ag3nt/src/bin/hive-ag3nt.rs b/hive-ag3nt/src/bin/hive-ag3nt.rs
index 6f899e65..ed9f32bc 100644
--- a/hive-ag3nt/src/bin/hive-ag3nt.rs
+++ b/hive-ag3nt/src/bin/hive-ag3nt.rs
@@ -4,7 +4,7 @@ use std::time::Duration;
 
 use anyhow::Result;
 use clap::{Parser, Subcommand};
-use hive_ag3nt::events::{Bus, LiveEvent};
+use hive_ag3nt::events::{Bus, LiveEvent, TurnState};
 use hive_ag3nt::login::{self, LoginState};
 use hive_ag3nt::{DEFAULT_SOCKET, DEFAULT_WEB_PORT, client, mcp, turn, web_ui};
 use hive_sh4re::{AgentRequest, AgentResponse};
@@ -126,6 +126,7 @@ async fn serve(
                     body: body.clone(),
                     unread,
                 });
+                bus.set_state(TurnState::Thinking);
                 let prompt = format_wake_prompt(&from, &body, unread);
                 let outcome = turn::drive_turn(
                     &prompt,
@@ -137,6 +138,7 @@ async fn serve(
                 )
                 .await;
                 turn::emit_turn_end(&bus, &outcome);
+                bus.set_state(TurnState::Idle);
             }
             Ok(AgentResponse::Empty) => {}
             Ok(AgentResponse::Ok | AgentResponse::Status { .. } | AgentResponse::Recent { .. }) => {
diff --git a/hive-ag3nt/src/bin/hive-m1nd.rs b/hive-ag3nt/src/bin/hive-m1nd.rs
index 06a61704..7d3113cf 100644
--- a/hive-ag3nt/src/bin/hive-m1nd.rs
+++ b/hive-ag3nt/src/bin/hive-m1nd.rs
@@ -8,7 +8,7 @@ use std::time::Duration;
 
 use anyhow::Result;
 use clap::{Parser, Subcommand};
-use hive_ag3nt::events::{Bus, LiveEvent};
+use hive_ag3nt::events::{Bus, LiveEvent, TurnState};
 use hive_ag3nt::login::{self, LoginState};
 use hive_ag3nt::{DEFAULT_SOCKET, DEFAULT_WEB_PORT, client, mcp, turn, web_ui};
 use hive_sh4re::{HelperEvent, ManagerRequest, ManagerResponse, SYSTEM_SENDER};
@@ -124,6 +124,7 @@ async fn serve(socket: &Path, interval: Duration, bus: Bus) -> Result<()> {
                     unread,
                 });
                 let prompt = format_wake_prompt(&from, &body, unread);
+                bus.set_state(TurnState::Thinking);
                 let outcome = turn::drive_turn(
                     &prompt,
                     &mcp_config,
@@ -134,6 +135,7 @@ async fn serve(socket: &Path, interval: Duration, bus: Bus) -> Result<()> {
                 )
                 .await;
                 turn::emit_turn_end(&bus, &outcome);
+                bus.set_state(TurnState::Idle);
             }
             Ok(ManagerResponse::Empty) => {}
             Ok(
diff --git a/hive-ag3nt/src/events.rs b/hive-ag3nt/src/events.rs
index 47ba13e3..40251370 100644
--- a/hive-ag3nt/src/events.rs
+++ b/hive-ag3nt/src/events.rs
@@ -24,6 +24,14 @@ const HISTORY_CAPACITY: usize = 2000;
 /// `HYPERHIVE_EVENTS_DB` env var (used in tests and one-shot tools).
 const DEFAULT_EVENTS_DB: &str = "/state/hyperhive-events.sqlite";
 
+fn now_unix() -> i64 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .ok()
+        .and_then(|d| i64::try_from(d.as_secs()).ok())
+        .unwrap_or(0)
+}
+
 const SCHEMA: &str = "
 CREATE TABLE IF NOT EXISTS events (
     id           INTEGER PRIMARY KEY AUTOINCREMENT,
@@ -116,6 +124,22 @@ impl EventStore {
     }
 }
 
+/// Authoritative turn-loop state. The harness owns it; the web UI
+/// reads via `/api/state` and renders. Lives alongside the bus
+/// because everyone who has a `Bus` already has the right handle to
+/// poke the state on transitions.
+#[derive(Debug, Clone, Copy, Serialize, PartialEq, Eq)]
+#[serde(rename_all = "snake_case")]
+pub enum TurnState {
+    /// Inbox is empty / waiting on `Recv`.
+    Idle,
+    /// `claude --print` is running for a turn.
+    Thinking,
+    /// Operator-triggered `/compact` is running on the persistent
+    /// session.
+    Compacting,
+}
+
 #[derive(Clone)]
 pub struct Bus {
     tx: Arc<broadcast::Sender<LiveEvent>>,
@@ -123,6 +147,8 @@ pub struct Bus {
     /// at construction — we keep going so the harness doesn't die on a
     /// missing `/state/` mount in dev / test scenarios.
     store: Option<Arc<EventStore>>,
+    /// Current turn-loop state + since-when (unix seconds).
+    state: Arc<Mutex<(TurnState, i64)>>,
 }
 
 impl Bus {
@@ -144,9 +170,26 @@ impl Bus {
         Self {
             tx: Arc::new(tx),
             store,
+            state: Arc::new(Mutex::new((TurnState::Idle, now_unix()))),
         }
     }
 
+    /// Update the harness's authoritative turn-loop state. Records
+    /// the transition time so `state_snapshot` can return a since-age.
+    pub fn set_state(&self, next: TurnState) {
+        let mut guard = self.state.lock().unwrap();
+        if guard.0 == next {
+            return;
+        }
+        *guard = (next, now_unix());
+    }
+
+    /// Current state + since-when (unix seconds). Snapshot copy, no lock held.
+    #[must_use]
+    pub fn state_snapshot(&self) -> (TurnState, i64) {
+        *self.state.lock().unwrap()
+    }
+
     pub fn emit(&self, event: LiveEvent) {
         if let Some(store) = &self.store
             && let Err(e) = store.append(&event)
diff --git a/hive-ag3nt/src/web_ui.rs b/hive-ag3nt/src/web_ui.rs
index 688f7a03..e03c7409 100644
--- a/hive-ag3nt/src/web_ui.rs
+++ b/hive-ag3nt/src/web_ui.rs
@@ -153,6 +153,11 @@ struct StateSnapshot {
     /// from the broker via the per-agent socket on each render.
     /// Empty on transport failure.
     inbox: Vec<hive_sh4re::InboxRow>,
+    /// Authoritative turn-loop state from the harness and the unix
+    /// timestamp the state was entered. The JS computes the age
+    /// client-side off this rather than tracking it from SSE events.
+    turn_state: crate::events::TurnState,
+    turn_state_since: i64,
 }
 
 #[derive(Serialize)]
@@ -187,12 +192,15 @@ async fn api_state(State(state): State<AppState>) -> axum::Json<StateSnapshot> {
         .and_then(|s| s.parse::<u16>().ok())
         .unwrap_or(7000);
     let inbox = recent_inbox(&state.socket, state.flavor).await;
+    let (turn_state, turn_state_since) = state.bus.state_snapshot();
     axum::Json(StateSnapshot {
         label: state.label.clone(),
         dashboard_port,
         status,
         session: session_view,
         inbox,
+        turn_state,
+        turn_state_since,
     })
 }
 
@@ -359,7 +367,10 @@ async fn post_compact(State(state): State<AppState>) -> Response {
                 return;
             }
         };
-        if let Err(e) = crate::turn::compact_session(&settings, &bus).await {
+        bus.set_state(crate::events::TurnState::Compacting);
+        let r = crate::turn::compact_session(&settings, &bus).await;
+        bus.set_state(crate::events::TurnState::Idle);
+        if let Err(e) = r {
             bus.emit(crate::events::LiveEvent::Note(format!(
                 "/compact failed: {e:#}"
             )));
diff --git a/hive-c0re/assets/app.js b/hive-c0re/assets/app.js
index 61ee03e5..3f9aff88 100644
--- a/hive-c0re/assets/app.js
+++ b/hive-c0re/assets/app.js
@@ -161,11 +161,66 @@
       }
       li.append(actions);
 
+      // Per-container journald viewer. Expand to fetch + render the
+      // last N lines; refresh button re-fetches; unit selector
+      // narrows to the harness service (or empty = full machine).
+      const journalUnit = c.is_manager ? 'hive-m1nd.service' : 'hive-ag3nt.service';
+      li.append(buildJournalDetails(c.container, journalUnit));
+
       ul.append(li);
     }
     root.append(ul);
   }
 
+  // Build the per-container journald <details>. Lazy-fetches when the
+  // operator expands; refresh re-fetches; unit toggle switches
+  // between the harness service and the full machine journal.
+  function buildJournalDetails(containerName, defaultUnit) {
+    const details = el('details', { class: 'journal' });
+    const summary = el('summary', {}, '↳ logs · ' + containerName);
+    const body = el('div', { class: 'journal-body' });
+    const controls = el('div', { class: 'journal-controls' });
+    const unitSelect = el('select', { class: 'journal-unit' });
+    unitSelect.append(
+      el('option', { value: defaultUnit }, defaultUnit),
+      el('option', { value: '' }, '(full machine journal)'),
+    );
+    const refresh = el('button', { type: 'button', class: 'btn btn-restart journal-refresh' },
+      '↻ refresh');
+    const pre = el('pre', { class: 'journal-output' }, 'fetching…');
+    let fetching = false;
+    async function fetchLogs() {
+      if (fetching) return;
+      fetching = true;
+      pre.textContent = 'fetching…';
+      const unit = unitSelect.value;
+      const params = new URLSearchParams({ lines: '500' });
+      if (unit) params.set('unit', unit);
+      try {
+        const resp = await fetch('/api/journal/' + containerName + '?' + params);
+        const text = await resp.text();
+        if (!resp.ok) {
+          pre.textContent = 'error: ' + resp.status + '\n' + text;
+        } else {
+          pre.textContent = text || '(empty)';
+          // Auto-scroll to bottom on fresh fetch.
+          pre.scrollTop = pre.scrollHeight;
+        }
+      } catch (err) {
+        pre.textContent = 'fetch failed: ' + err;
+      } finally {
+        fetching = false;
+      }
+    }
+    details.addEventListener('toggle', () => { if (details.open) fetchLogs(); });
+    refresh.addEventListener('click', (e) => { e.preventDefault(); fetchLogs(); });
+    unitSelect.addEventListener('change', fetchLogs);
+    controls.append(unitSelect, refresh);
+    body.append(controls, pre);
+    details.append(summary, body);
+    return details;
+  }
+
   function renderTombstones(s) {
     const root = $('tombstones-section');
     root.innerHTML = '';
diff --git a/hive-c0re/assets/dashboard.css b/hive-c0re/assets/dashboard.css
index b48cac30..d1a1841b 100644
--- a/hive-c0re/assets/dashboard.css
+++ b/hive-c0re/assets/dashboard.css
@@ -143,6 +143,53 @@ a:hover {
   opacity: 0.85;
 }
 .container-row.tombstone .name { color: var(--muted); }
+/* Per-container journald viewer: collapsed by default, fetches
+   lazily on expand. The output is in monospace inside a bordered
+   <pre>; controls (unit select + refresh) sit above. */
+.journal {
+  margin-top: 0.5em;
+  font-size: 0.85em;
+}
+.journal > summary {
+  cursor: pointer;
+  color: var(--muted);
+  letter-spacing: 0.05em;
+}
+.journal > summary:hover { color: var(--cyan); }
+.journal .journal-body {
+  margin-top: 0.4em;
+  padding-top: 0.4em;
+  border-top: 1px dashed var(--border);
+}
+.journal-controls {
+  display: flex;
+  gap: 0.5em;
+  margin-bottom: 0.4em;
+  align-items: center;
+}
+.journal-unit {
+  font-family: inherit;
+  font-size: 0.9em;
+  background: var(--bg-elev);
+  color: var(--fg);
+  border: 1px solid var(--border);
+  padding: 0.2em 0.4em;
+}
+.journal-refresh { font-size: 0.75em; padding: 0.15em 0.5em; }
+.journal-output {
+  margin: 0;
+  background: #11111b;
+  color: var(--fg);
+  border: 1px solid var(--purple-dim);
+  padding: 0.5em 0.7em;
+  max-height: 24em;
+  overflow: auto;
+  font-size: 0.85em;
+  line-height: 1.4;
+  white-space: pre;
+  word-break: normal;
+}
+
 .pending-state {
   color: var(--amber);
   font-size: 0.85em;
diff --git a/hive-c0re/src/dashboard.rs b/hive-c0re/src/dashboard.rs
index 1165e990..6430d7c6 100644
--- a/hive-c0re/src/dashboard.rs
+++ b/hive-c0re/src/dashboard.rs
@@ -53,6 +53,7 @@ pub async fn serve(port: u16, coord: Arc<Coordinator>) -> Result<()> {
         .route("/answer-question/{id}", post(post_answer_question))
         .route("/cancel-question/{id}", post(post_cancel_question))
         .route("/purge-tombstone/{name}", post(post_purge_tombstone))
+        .route("/api/journal/{name}", get(get_journal))
         .route("/request-spawn", post(post_request_spawn))
         .route("/messages/stream", get(messages_stream))
         .with_state(AppState { coord });
@@ -467,6 +468,76 @@ async fn post_cancel_question(
     }
 }
 
+#[derive(Deserialize)]
+struct JournalQuery {
+    /// Optional systemd unit filter — e.g. `hive-ag3nt.service`. When
+    /// omitted, returns the full machine journal.
+    #[serde(default)]
+    unit: Option<String>,
+    /// Number of trailing lines to return. Capped at 5000.
+    #[serde(default)]
+    lines: Option<u32>,
+}
+
+/// Shell out to `journalctl -M <container> -b` and return its text
+/// output. Operator-only by virtue of the dashboard being host-bound;
+/// hive-c0re already runs as root in its systemd unit so journalctl
+/// has the access it needs.
+async fn get_journal(
+    AxumPath(name): AxumPath<String>,
+    axum::extract::Query(q): axum::extract::Query<JournalQuery>,
+) -> Response {
+    // Validate the container name against the list of managed
+    // containers so we don't shell out with arbitrary input.
+    let container = strip_container_prefix(&name);
+    let prefixed = if container == lifecycle::MANAGER_NAME {
+        container.clone()
+    } else {
+        format!("{}{container}", lifecycle::AGENT_PREFIX)
+    };
+    let live = lifecycle::list().await.unwrap_or_default();
+    if !live.iter().any(|c| c == &prefixed) {
+        return error_response(&format!("journal: no managed container {prefixed:?}"));
+    }
+    let lines = q.lines.unwrap_or(500).min(5000);
+    let mut cmd = tokio::process::Command::new("journalctl");
+    cmd.args([
+        "-M",
+        &prefixed,
+        "-b",
+        "--no-pager",
+        "--output=short-iso",
+        "--lines",
+    ])
+    .arg(lines.to_string());
+    if let Some(u) = q.unit.as_deref().filter(|s| !s.is_empty()) {
+        // accept hive-ag3nt[.service] / hive-m1nd[.service] — anything
+        // else we refuse, again to keep the shell-out tight.
+        let allowed = ["hive-ag3nt.service", "hive-m1nd.service"];
+        let unit = if u.ends_with(".service") {
+            u.to_owned()
+        } else {
+            format!("{u}.service")
+        };
+        if !allowed.contains(&unit.as_str()) {
+            return error_response(&format!("journal: unknown unit {unit:?}"));
+        }
+        cmd.args(["-u", &unit]);
+    }
+    match cmd.output().await {
+        Ok(out) => {
+            // Combine stdout + stderr — journalctl emits to both on errors.
+            let mut body = String::from_utf8_lossy(&out.stdout).into_owned();
+            if !out.status.success() {
+                body.push_str("\n--- stderr ---\n");
+                body.push_str(&String::from_utf8_lossy(&out.stderr));
+            }
+            ([("content-type", "text/plain; charset=utf-8")], body).into_response()
+        }
+        Err(e) => error_response(&format!("journalctl spawn: {e}")),
+    }
+}
+
 async fn post_purge_tombstone(
     State(state): State<AppState>,
     AxumPath(name): AxumPath<String>,
diff --git a/hive-c0re/src/lifecycle.rs b/hive-c0re/src/lifecycle.rs
index 985b82d0..f6757351 100644
--- a/hive-c0re/src/lifecycle.rs
+++ b/hive-c0re/src/lifecycle.rs
@@ -45,14 +45,51 @@ const WEB_PORT_RANGE: u16 = 900;
 const DEFAULT_MEMORY_MAX: &str = "2G";
 const DEFAULT_CPU_QUOTA: &str = "50%";
 
-/// Returns the per-agent web UI port. Same hash on both sides — manager,
-/// dashboard, and agent harness all agree. Manager is fixed at
-/// `MANAGER_PORT`.
+/// Returns the per-agent web UI port. Manager is fixed at `MANAGER_PORT`.
+/// For sub-agents the port is sticky once chosen: looked up from
+/// `agent_state_root(name)/port` if present, otherwise derived from
+/// the FNV-1a hash of the name and *probed forward* through the
+/// allocated range to skip any port another sub-agent has already
+/// claimed (birthday-paradox collisions are real even at 2–3
+/// agents). The chosen port is written back so subsequent calls
+/// resolve to the same value without re-probing.
 #[must_use]
 pub fn agent_web_port(name: &str) -> u16 {
     if name == MANAGER_NAME {
         return MANAGER_PORT;
     }
+    let state_root = crate::coordinator::Coordinator::agent_state_root(name);
+    let port_file = state_root.join("port");
+    if let Ok(s) = std::fs::read_to_string(&port_file)
+        && let Ok(port) = s.trim().parse::<u16>()
+        && (WEB_PORT_BASE..WEB_PORT_BASE + WEB_PORT_RANGE).contains(&port)
+    {
+        return port;
+    }
+    let taken = scan_taken_ports(name);
+    let start = port_hash(name);
+    let mut port = start;
+    for _ in 0..WEB_PORT_RANGE {
+        if !taken.contains(&port) {
+            break;
+        }
+        port = next_port(port);
+        if port == start {
+            // Range fully exhausted (very unlikely — 900 slots) —
+            // give up and just use the hashed value; collisions are
+            // surfaced as bind errors by the harness retry loop.
+            tracing::warn!(%name, "agent_web_port: range exhausted, returning hash");
+            return start;
+        }
+    }
+    let _ = std::fs::create_dir_all(&state_root);
+    if let Err(e) = std::fs::write(&port_file, format!("{port}\n")) {
+        tracing::warn!(error = ?e, file = %port_file.display(), "persisting agent port failed");
+    }
+    port
+}
+
+fn port_hash(name: &str) -> u16 {
     let mut hash: u32 = 2_166_136_261;
     for b in name.bytes() {
         hash ^= u32::from(b);
@@ -62,6 +99,48 @@ pub fn agent_web_port(name: &str) -> u16 {
     WEB_PORT_BASE + u16::try_from(hash % u32::from(WEB_PORT_RANGE)).unwrap_or(0)
 }
 
+fn next_port(port: u16) -> u16 {
+    let p = port + 1;
+    if p >= WEB_PORT_BASE + WEB_PORT_RANGE {
+        WEB_PORT_BASE
+    } else {
+        p
+    }
+}
+
+/// Scan every other agent's effective web UI port: prefer the
+/// persisted `port` file when present, fall back to the hashed
+/// value for legacy agents that pre-date the port-file scheme. The
+/// latter is important on existing deployments — without it, a new
+/// agent's collision check wouldn't see incumbents that haven't
+/// written their port file yet, and we'd re-emit the same
+/// collision the operator just hit.
+fn scan_taken_ports(name: &str) -> std::collections::HashSet<u16> {
+    let mut out = std::collections::HashSet::new();
+    let Ok(rd) = std::fs::read_dir("/var/lib/hyperhive/agents") else {
+        return out;
+    };
+    for entry in rd.flatten() {
+        let Ok(file_name) = entry.file_name().into_string() else {
+            continue;
+        };
+        if file_name == name || file_name == MANAGER_NAME {
+            continue;
+        }
+        let pf = entry.path().join("port");
+        if let Ok(s) = std::fs::read_to_string(&pf)
+            && let Ok(port) = s.trim().parse::<u16>()
+        {
+            out.insert(port);
+        } else {
+            // Legacy: no port file yet → its effective port is the
+            // bare hash. Treat as taken so we don't collide with it.
+            out.insert(port_hash(&file_name));
+        }
+    }
+    out
+}
+
 #[must_use]
 pub fn container_name(name: &str) -> String {
     if name == MANAGER_NAME {