fix(host-detail): switch host resource to LocalResource to fix hydration mismatch

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.toml

@@ -6,6 +6,15 @@ edition = "2021"
 # Leptos nécessite deux formats de compilation :
 # - rlib   : bibliothèque normale, utilisée par le serveur Axum
 # - cdylib : bibliothèque dynamique compilée en WebAssembly pour le navigateur
+[[bin]]
+name = "rust-ipam"
+path = "src/main.rs"
+
+[[bin]]
+name = "seed"
+path = "src/bin/seed.rs"
+required-features = ["ssr"]
+
 [lib]
 crate-type = ["cdylib", "rlib"]
 

migrations/postgres/0008_create_host_applications.sql

@@ -0,0 +1,8 @@
+-- host_applications: direct association between a host and an application.
+-- Allows explicitly tagging a host with an application regardless of ports.
+-- One application can only be linked once to a given host.
+CREATE TABLE IF NOT EXISTS host_applications (
+    host_id        BIGINT NOT NULL REFERENCES hosts(id)        ON DELETE CASCADE,
+    application_id BIGINT NOT NULL REFERENCES applications(id) ON DELETE CASCADE,
+    PRIMARY KEY (host_id, application_id)
+);

migrations/sqlite/0008_create_host_applications.sql

@@ -0,0 +1,8 @@
+-- host_applications: direct association between a host and an application.
+-- Allows explicitly tagging a host with an application regardless of ports.
+-- One application can only be linked once to a given host.
+CREATE TABLE IF NOT EXISTS host_applications (
+    host_id        INTEGER NOT NULL REFERENCES hosts(id)        ON DELETE CASCADE,
+    application_id INTEGER NOT NULL REFERENCES applications(id) ON DELETE CASCADE,
+    PRIMARY KEY (host_id, application_id)
+);

src/api/hosts.rs

@@ -3,9 +3,7 @@
 use leptos::prelude::*;
 use serde::{Deserialize, Serialize};
 
-use crate::models::Host;
-
-use crate::models::Port;
+use crate::models::{Application, Host, Port};
 
 // ─── Presentation types ───────────────────────────────────────────────────────
 
@@ -32,7 +30,7 @@ pub struct HostsPage {
     pub total_pages: i64, // ceil(total / per_page); always ≥ 1
 }
 
-// Full host detail: identity fields + resolved network + open ports.
+// Full host detail: identity fields + resolved network + open ports + linked applications.
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub struct HostDetail {
     pub id: i64,
@@ -42,6 +40,7 @@ pub struct HostDetail {
     pub network_name: String,
     pub network_cidr: String,
     pub ports: Vec<Port>,
+    pub applications: Vec<Application>,
 }
 
 // ─── Queries ──────────────────────────────────────────────────────────────────
@@ -50,7 +49,12 @@ pub struct HostDetail {
 #[server]
 pub async fn get_host_detail(id: i64) -> Result<HostDetail, ServerFnError> {
     use sqlx::AnyPool;
-    use crate::server::repository::{hosts as host_repo, networks, ports as port_repo};
+    use crate::server::repository::{
+        applications as app_repo,
+        hosts as host_repo,
+        networks,
+        ports as port_repo,
+    };
 
     let pool = use_context::<AnyPool>()
         .ok_or_else(|| ServerFnError::new("Database pool not found in context"))?;
@@ -69,6 +73,10 @@ pub async fn get_host_detail(id: i64) -> Result<HostDetail, ServerFnError> {
         .await
         .map_err(|e| ServerFnError::new(e.to_string()))?;
 
+    let applications = app_repo::list_applications_for_host(&pool, id)
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))?;
+
     Ok(HostDetail {
         id: host.id,
         name: host.name,
@@ -77,6 +85,7 @@ pub async fn get_host_detail(id: i64) -> Result<HostDetail, ServerFnError> {
         network_name: network.name,
         network_cidr: network.cidr,
         ports,
+        applications,
     })
 }
 
@@ -343,6 +352,72 @@ pub async fn remove_host_port(host_id: i64, port_number: i64) -> Result<(), Serv
         .map_err(|e| ServerFnError::new(e.to_string()))
 }
 
+/// Returns all applications not yet directly linked to a host.
+///
+/// Used to populate the "add applications" modal on the host detail page.
+#[server]
+pub async fn get_applications_not_on_host(
+    host_id: i64,
+) -> Result<Vec<Application>, ServerFnError> {
+    use sqlx::AnyPool;
+    use crate::server::repository::applications as repo;
+
+    let pool = use_context::<AnyPool>()
+        .ok_or_else(|| ServerFnError::new("Database pool not found in context"))?;
+
+    repo::list_applications_not_on_host(&pool, host_id)
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))
+}
+
+/// Links one or more applications to a host.
+///
+/// `application_ids` is a comma-separated string of application IDs (e.g. "1,3,7").
+/// Already-linked applications are silently skipped (no-op).
+#[server]
+pub async fn add_host_applications(
+    host_id: i64,
+    application_ids: String,
+) -> Result<(), ServerFnError> {
+    use sqlx::AnyPool;
+    use crate::server::repository::applications as repo;
+
+    let pool = use_context::<AnyPool>()
+        .ok_or_else(|| ServerFnError::new("Database pool not found in context"))?;
+
+    let ids: Vec<i64> = application_ids
+        .split(',')
+        .filter_map(|s| s.trim().parse::<i64>().ok())
+        .collect();
+
+    for application_id in ids {
+        repo::add_application_to_host(&pool, host_id, application_id)
+            .await
+            .map_err(|e| ServerFnError::new(e.to_string()))?;
+    }
+
+    Ok(())
+}
+
+/// Removes the direct link between a host and an application.
+///
+/// Returns `true` if the association existed and was removed.
+#[server]
+pub async fn remove_host_application(
+    host_id: i64,
+    application_id: i64,
+) -> Result<bool, ServerFnError> {
+    use sqlx::AnyPool;
+    use crate::server::repository::applications as repo;
+
+    let pool = use_context::<AnyPool>()
+        .ok_or_else(|| ServerFnError::new("Database pool not found in context"))?;
+
+    repo::remove_application_from_host(&pool, host_id, application_id)
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))
+}
+
 /// Deletes a host by id.
 ///
 /// Also removes all its port associations (via `ON DELETE CASCADE`).

src/client/host_detail.rs

@@ -1,17 +1,177 @@
 // client/host_detail.rs — Host detail page
 //
 // Shows all information for a single host:
-//   - Identity form  : name, IP, network dropdown — editable, saved with "Save changes"
-//   - Ports section  : full list with Remove per port + Add port input
-//   - Delete button  : opens a confirmation modal, then navigates back to /hosts
+//   - Identity form     : name, IP, network dropdown — editable, saved with "Save changes"
+//   - Ports section     : full list with Remove per port + Add port input
+//   - Applications      : directly linked apps with Remove + modal multi-select to add
+//   - Delete button     : opens a confirmation modal, then navigates back to /hosts
 
 use leptos::prelude::*;
 use leptos_router::hooks::{use_navigate, use_params_map, use_query_map};
 
 use crate::api::{
-    hosts::{AddHostPort, DeleteHost, RemoveHostPort, UpdateHost, get_host_detail},
+    hosts::{
+        AddHostApplications, AddHostPort, DeleteHost, RemoveHostApplication,
+        RemoveHostPort, UpdateHost, get_applications_not_on_host, get_host_detail,
+    },
     networks::get_networks,
 };
+use crate::models::Application;
+
+// ─── Add applications modal ───────────────────────────────────────────────────
+
+// Scrollable pick list + selected tags:
+//   - Top: scrollable list of available apps; clicking one moves it to the
+//     selected section and removes it from the list.
+//   - Bottom: selected apps shown as removable tags; clicking × puts the app
+//     back in the list.
+//
+// The auto-close Effect lives in the PARENT to avoid the re-trigger bug
+// (an Effect inside a conditionally-rendered component fires on mount and
+// would immediately close the modal if the action already held a past Ok value).
+#[component]
+fn AddAppModal(
+    host_id: i64,
+    available_apps_res: LocalResource<Result<Vec<Application>, ServerFnError>>,
+    add_action: ServerAction<AddHostApplications>,
+    show_modal: RwSignal<bool>,
+) -> impl IntoView {
+    // Full Application structs so names are available in the selected tag list.
+    let selected: RwSignal<Vec<Application>> = RwSignal::new(vec![]);
+
+    view! {
+        <div class="modal-backdrop" on:click=move |_| show_modal.set(false)>
+            <div class="modal" on:click=move |e| e.stop_propagation()>
+                <div class="modal__header">
+                    <h2>"Add applications"</h2>
+                    <button class="modal__close" type="button" aria-label="Close"
+                        on:click=move |_| show_modal.set(false)>
+                        "×"
+                    </button>
+                </div>
+
+                <div class="modal__body">
+
+                    // ── Scrollable pick list ──────────────────────────────────
+                    {move || match available_apps_res.get() {
+                        None => view! { <p class="empty">"Loading…"</p> }.into_any(),
+                        Some(r) => match (*r).clone() {
+                            Err(e) => view! {
+                                <p class="error">
+                                    "Could not load applications: " {e.to_string()}
+                                </p>
+                            }.into_any(),
+                            Ok(apps) => {
+                                // Exclude already-selected apps from the displayed list.
+                                let sel_ids: Vec<i64> = selected.get()
+                                    .iter().map(|a| a.id).collect();
+                                let displayed: Vec<Application> = apps.into_iter()
+                                    .filter(|a| !sel_ids.contains(&a.id))
+                                    .collect();
+
+                                if displayed.is_empty() && sel_ids.is_empty() {
+                                    view! {
+                                        <p class="empty">
+                                            "All applications are already linked to this host."
+                                        </p>
+                                    }.into_any()
+                                } else if displayed.is_empty() {
+                                    view! {
+                                        <p class="empty">
+                                            "All available applications have been selected."
+                                        </p>
+                                    }.into_any()
+                                } else {
+                                    view! {
+                                        <ul class="app-pick-list">
+                                            {displayed.into_iter().map(|app| {
+                                                let app_clone = app.clone();
+                                                view! {
+                                                    <li class="app-pick-item"
+                                                        on:click=move |_| {
+                                                            selected.update(|v| {
+                                                                v.push(app_clone.clone());
+                                                            });
+                                                        }
+                                                    >
+                                                        <span>{app.name}</span>
+                                                        <span class="app-pick-item__add">"+"</span>
+                                                    </li>
+                                                }
+                                            }).collect_view()}
+                                        </ul>
+                                    }.into_any()
+                                }
+                            }
+                        }
+                    }}
+
+                    // ── Selected tags (shown once at least one app is chosen) ─
+                    {move || (!selected.get().is_empty()).then(|| {
+                        let sel = selected.get();
+                        view! {
+                            <div class="app-selected-section">
+                                <span class="app-selected-label">"Selected:"</span>
+                                <div class="app-selected-list">
+                                    {sel.into_iter().map(|app| {
+                                        let app_id = app.id;
+                                        view! {
+                                            <span class="app-selected-tag">
+                                                {app.name}
+                                                <button
+                                                    class="app-selected-tag__remove"
+                                                    type="button"
+                                                    aria-label="Remove"
+                                                    on:click=move |_| {
+                                                        selected.update(|v| {
+                                                            v.retain(|x| x.id != app_id);
+                                                        });
+                                                    }
+                                                >"×"</button>
+                                            </span>
+                                        }
+                                    }).collect_view()}
+                                </div>
+                            </div>
+                        }
+                    })}
+
+                    {move || add_action.value().get()
+                        .and_then(|r| r.err())
+                        .map(|e| view! { <p class="error">{e.to_string()}</p> })
+                    }
+                </div>
+
+                <div class="modal__actions">
+                    <button class="btn-secondary" type="button"
+                        on:click=move |_| show_modal.set(false)>
+                        "Cancel"
+                    </button>
+                    <button
+                        class="btn-primary"
+                        type="button"
+                        disabled={move || selected.get().is_empty()}
+                        on:click=move |_| {
+                            let ids_str = selected.get_untracked()
+                                .iter()
+                                .map(|a| a.id.to_string())
+                                .collect::<Vec<_>>()
+                                .join(",");
+                            if !ids_str.is_empty() {
+                                add_action.dispatch(AddHostApplications {
+                                    host_id,
+                                    application_ids: ids_str,
+                                });
+                            }
+                        }
+                    >
+                        "Add selected"
+                    </button>
+                </div>
+            </div>
+        </div>
+    }.into_any()
+}
 
 // ─── Delete confirmation modal ────────────────────────────────────────────────
 
@@ -36,7 +196,7 @@ fn DeleteModal(
                     <p class="warning">
                         "Are you sure you want to delete "
                         <strong>{host_name}</strong>
-                        "? All port associations will also be removed."
+                        "? All port and application associations will also be removed."
                     </p>
                 </div>
                 <div class="modal__actions">
@@ -58,8 +218,6 @@ fn DeleteModal(
 
 #[component]
 pub fn HostDetailPage() -> impl IntoView {
-    // Read the `:id` segment from the URL.
-    // `use_params_map()` returns a reactive map of all URL path parameters.
     let params = use_params_map();
     let host_id = move || {
         params.read().get("id")
@@ -67,8 +225,6 @@ pub fn HostDetailPage() -> impl IntoView {
             .unwrap_or(0)
     };
 
-    // Optional `?back=<url>` query parameter — used when arriving from a network
-    // detail page so the back button returns there instead of the hosts list.
     let query = use_query_map();
     let back_url = move || {
         query.read().get("back")
@@ -82,47 +238,64 @@ pub fn HostDetailPage() -> impl IntoView {
     let update_action      = ServerAction::<UpdateHost>::new();
     let add_port_action    = ServerAction::<AddHostPort>::new();
     let remove_port_action = ServerAction::<RemoveHostPort>::new();
+    let add_app_action     = ServerAction::<AddHostApplications>::new();
+    let remove_app_action  = ServerAction::<RemoveHostApplication>::new();
     let delete_action      = ServerAction::<DeleteHost>::new();
 
-    let show_delete_modal = RwSignal::new(false);
+    let show_delete_modal  = RwSignal::new(false);
+    let show_add_app_modal = RwSignal::new(false);
 
-    // Reload detail after any mutation that touches this host.
-    // The resource key includes action versions so it invalidates automatically.
-    let host = Resource::new(
-        move || (
-            host_id(),
-            update_action.version().get(),
-            add_port_action.version().get(),
-            remove_port_action.version().get(),
-        ),
-        |(id, _, _, _)| get_host_detail(id),
-    );
+    // Auto-close the add-app modal after a successful addition.
+    // Keeping this Effect in the parent avoids the re-trigger bug that would
+    // occur if the Effect were inside AddAppModal (it would fire on mount
+    // if the action already held a previous Ok value).
+    Effect::new(move |_| {
+        if let Some(Ok(_)) = add_app_action.value().get() {
+            show_add_app_modal.set(false);
+        }
+    });
+
+    // LocalResource avoids reading the resource outside <Suspense> during hydration,
+    // which would cause a mismatch between the SSR-rendered fallback and the content
+    // the WASM expects to find after the resource resolves.
+    let host = LocalResource::new(move || {
+        let _ = update_action.version().get();
+        let _ = add_port_action.version().get();
+        let _ = remove_port_action.version().get();
+        let _ = add_app_action.version().get();
+        let _ = remove_app_action.version().get();
+        get_host_detail(host_id())
+    });
 
     // Networks dropdown — LocalResource avoids SSR/hydration mismatch.
     let networks_res = LocalResource::new(|| get_networks());
 
-    // Edit-field signals, populated once by the Effect below.
-    // Using signals (rather than local variables) keeps them stable across
-    // re-renders and lets the user edit without triggering a resource reload.
+    // Available apps for the modal: re-fetched whenever add/remove completes.
+    let add_app_ver    = add_app_action.version();
+    let remove_app_ver = remove_app_action.version();
+    let available_apps_res = LocalResource::new(move || {
+        let _ = add_app_ver.get();
+        let _ = remove_app_ver.get();
+        get_applications_not_on_host(host_id())
+    });
+
     let name_sig   = RwSignal::new(String::new());
     let ip_sig     = RwSignal::new(String::new());
     let net_id_sig = RwSignal::new(0i64);
+    let new_port   = RwSignal::new(String::new());
 
-    // Input value for the "add port" row.
-    let new_port = RwSignal::new(String::new());
-
-    // Sync edit signals whenever the host resource delivers fresh data.
-    // This runs on initial load and after every successful mutation.
+    // Sync edit signals whenever fresh host data arrives.
+    // LocalResource wraps its value in SendWrapper, so we dereference with `*r`.
     Effect::new(move |_| {
-        if let Some(Ok(ref detail)) = host.get() {
-            name_sig.set(detail.name.clone());
-            ip_sig.set(detail.ip.clone());
-            net_id_sig.set(detail.network_id);
+        if let Some(r) = host.get() {
+            if let Ok(ref detail) = *r {
+                name_sig.set(detail.name.clone());
+                ip_sig.set(detail.ip.clone());
+                net_id_sig.set(detail.network_id);
+            }
         }
     });
 
-    // Navigate back to the list after a successful delete.
-    // `use_navigate()` must be called during component setup (not inside a closure).
     let navigate = use_navigate();
     Effect::new(move |_| {
         if let Some(Ok(true)) = delete_action.value().get() {
@@ -133,16 +306,18 @@ pub fn HostDetailPage() -> impl IntoView {
     view! {
         <div class="host-detail-page">
             <Suspense fallback=|| view! { <p class="empty">"Loading host…"</p> }>
-                {move || host.get().map(|result| match result {
+                {move || host.get().map(|r| match (*r).clone() {
                     Err(e) => view! {
                         <p class="error">"Could not load host: " {e.to_string()}</p>
                     }.into_any(),
 
                     Ok(detail) => {
-                        let id          = detail.id;
-                        let modal_name  = detail.name.clone();
-                        let port_count  = detail.ports.len();
-                        let ports       = detail.ports;
+                        let id           = detail.id;
+                        let modal_name   = detail.name.clone();
+                        let port_count   = detail.ports.len();
+                        let app_count    = detail.applications.len();
+                        let ports        = detail.ports;
+                        let applications = detail.applications;
 
                         // Pre-built ports view — consumes `ports` once, not reactively.
                         let ports_list = if ports.is_empty() {
@@ -178,6 +353,37 @@ pub fn HostDetailPage() -> impl IntoView {
                             }.into_any()
                         };
 
+                        // Pre-built applications view.
+                        let apps_list = if applications.is_empty() {
+                            view! {
+                                <p class="empty">"No applications linked to this host."</p>
+                            }.into_any()
+                        } else {
+                            view! {
+                                <div class="app-list">
+                                    {applications.into_iter().map(|app| {
+                                        let app_id = app.id;
+                                        view! {
+                                            <div class="app-row">
+                                                <span class="app-row__name">{app.name}</span>
+                                                <button
+                                                    class="btn-danger"
+                                                    type="button"
+                                                    on:click=move |_| {
+                                                        remove_app_action.dispatch(
+                                                            RemoveHostApplication { host_id: id, application_id: app_id }
+                                                        );
+                                                    }
+                                                >
+                                                    "Remove"
+                                                </button>
+                                            </div>
+                                        }
+                                    }).collect_view()}
+                                </div>
+                            }.into_any()
+                        };
+
                         view! {
                             // ── Page header ──────────────────────────────────
                             <div class="page-header detail-page-header">
@@ -244,13 +450,13 @@ pub fn HostDetailPage() -> impl IntoView {
                                             class="btn-primary"
                                             type="button"
                                             on:click=move |_| {
-                                            update_action.dispatch(UpdateHost {
-                                                id,
-                                                name:       name_sig.get_untracked(),
-                                                ip:         ip_sig.get_untracked(),
-                                                network_id: net_id_sig.get_untracked(),
-                                            });
-                                        }
+                                                update_action.dispatch(UpdateHost {
+                                                    id,
+                                                    name:       name_sig.get_untracked(),
+                                                    ip:         ip_sig.get_untracked(),
+                                                    network_id: net_id_sig.get_untracked(),
+                                                });
+                                            }
                                         >
                                             "Save changes"
                                         </button>
@@ -273,7 +479,6 @@ pub fn HostDetailPage() -> impl IntoView {
                                     })
                                 }
 
-                                // Add port row
                                 <div class="port-add-row">
                                     <input
                                         type="number"
@@ -310,7 +515,43 @@ pub fn HostDetailPage() -> impl IntoView {
                                 </div>
                             </section>
 
-                            // ── Danger zone ──────────────────────────────────
+                            // ── Applications section ──────────────────────────
+                            <section class="detail-section">
+                                <h2 class="detail-section__title">
+                                    {format!("Applications ({})", app_count)}
+                                </h2>
+
+                                {apps_list}
+
+                                {move || remove_app_action.value().get()
+                                    .and_then(|r| r.err())
+                                    .map(|e| view! {
+                                        <p class="error">"Remove failed: " {e.to_string()}</p>
+                                    })
+                                }
+
+                                <div class="port-add-row">
+                                    <button
+                                        class="btn-primary"
+                                        type="button"
+                                        on:click=move |_| show_add_app_modal.set(true)
+                                    >
+                                        "+ Add applications"
+                                    </button>
+                                </div>
+                            </section>
+
+                            // ── Add applications modal ────────────────────────
+                            {move || show_add_app_modal.get().then(|| view! {
+                                <AddAppModal
+                                    host_id=id
+                                    available_apps_res=available_apps_res
+                                    add_action=add_app_action
+                                    show_modal=show_add_app_modal
+                                />
+                            })}
+
+                            // ── Danger zone ───────────────────────────────────
                             <div class="danger-zone">
                                 <button
                                     class="btn-danger-solid"

src/client/hosts.rs

@@ -287,12 +287,12 @@ fn PaginationBar(
 
 #[component]
 fn HostTable(
-    hosts: Resource<Result<HostsPageData, ServerFnError>>,
+    hosts: LocalResource<Result<HostsPageData, ServerFnError>>,
     pending_delete: RwSignal<Option<(i64, String)>>,
 ) -> impl IntoView {
     view! {
         <Suspense fallback=|| view! { <p class="empty">"Loading hosts…"</p> }>
-            {move || hosts.get().map(|result| match result {
+            {move || hosts.get().map(|r| match (*r).clone() {
                 Err(e) => view! {
                     <p class="error">"Could not load hosts: " {e.to_string()}</p>
                 }.into_any(),
@@ -380,28 +380,30 @@ pub fn HostsPage() -> impl IntoView {
     let page     = RwSignal::new(1i64);
     let per_page = RwSignal::new(15i64);
 
-    let hosts = Resource::new(
-        move || (
+    // LocalResource avoids reading a resource outside <Suspense> during hydration.
+    // All dependencies (filters, pagination, action versions) are client-side only,
+    // so there is no benefit to SSR for this resource.
+    let hosts = LocalResource::new(move || {
+        let _ = create_action.version().get();
+        let _ = delete_action.version().get();
+        get_hosts_page(
             name_filter.get(),
             network_id_filter.get(),
             port_filter.get(),
             app_id_filter.get(),
             page.get(),
             per_page.get(),
-            create_action.version().get(),
-            delete_action.version().get(),
-        ),
-        |(name, net, port, app, p, pp, _, _)| get_hosts_page(name, net, port, app, p, pp),
-    );
+        )
+    });
 
     let networks_res     = LocalResource::new(|| get_networks());
     let applications_res = LocalResource::new(|| get_applications());
 
     let total_pages = Signal::derive(move || {
-        hosts.get().and_then(|r| r.ok()).map(|p| p.total_pages).unwrap_or(1)
+        hosts.get().and_then(|r| (*r).clone().ok()).map(|p| p.total_pages).unwrap_or(1)
     });
     let total = Signal::derive(move || {
-        hosts.get().and_then(|r| r.ok()).map(|p| p.total).unwrap_or(0)
+        hosts.get().and_then(|r| (*r).clone().ok()).map(|p| p.total).unwrap_or(0)
     });
 
     view! {

src/server/repository/applications.rs

@@ -54,6 +54,84 @@ pub async fn delete_application(pool: &AnyPool, id: i64) -> Result<bool, DbError
     Ok(result.rows_affected() > 0)
 }
 
+// ─── Host-application associations ───────────────────────────────────────────
+
+/// Returns all applications linked directly to a host, ordered by name.
+pub async fn list_applications_for_host(
+    pool: &AnyPool,
+    host_id: i64,
+) -> Result<Vec<Application>, DbError> {
+    let rows = sqlx::query(
+        "SELECT a.id, a.name
+         FROM applications a
+         JOIN host_applications ha ON ha.application_id = a.id
+         WHERE ha.host_id = $1
+         ORDER BY a.name",
+    )
+    .bind(host_id)
+    .fetch_all(pool)
+    .await?;
+    Ok(rows.iter().map(row_to_application).collect())
+}
+
+/// Returns all applications NOT yet linked to a host, ordered by name.
+pub async fn list_applications_not_on_host(
+    pool: &AnyPool,
+    host_id: i64,
+) -> Result<Vec<Application>, DbError> {
+    let rows = sqlx::query(
+        "SELECT id, name FROM applications
+         WHERE id NOT IN (
+             SELECT application_id FROM host_applications WHERE host_id = $1
+         )
+         ORDER BY name",
+    )
+    .bind(host_id)
+    .fetch_all(pool)
+    .await?;
+    Ok(rows.iter().map(row_to_application).collect())
+}
+
+/// Links an application directly to a host.
+///
+/// If the link already exists, this is a no-op (not an error).
+pub async fn add_application_to_host(
+    pool: &AnyPool,
+    host_id: i64,
+    application_id: i64,
+) -> Result<(), DbError> {
+    let result = sqlx::query(
+        "INSERT INTO host_applications (host_id, application_id) VALUES ($1, $2)",
+    )
+    .bind(host_id)
+    .bind(application_id)
+    .execute(pool)
+    .await;
+    match result {
+        Ok(_) => Ok(()),
+        Err(sqlx::Error::Database(ref e)) if e.is_unique_violation() => Ok(()),
+        Err(e) => Err(DbError::Connection(e)),
+    }
+}
+
+/// Removes the direct link between a host and an application.
+///
+/// Returns `true` if the association existed and was removed.
+pub async fn remove_application_from_host(
+    pool: &AnyPool,
+    host_id: i64,
+    application_id: i64,
+) -> Result<bool, DbError> {
+    let result = sqlx::query(
+        "DELETE FROM host_applications WHERE host_id = $1 AND application_id = $2",
+    )
+    .bind(host_id)
+    .bind(application_id)
+    .execute(pool)
+    .await?;
+    Ok(result.rows_affected() > 0)
+}
+
 // ─── Application-port associations ───────────────────────────────────────────
 
 /// Returns all port numbers associated with an application, sorted numerically.

style/rust-ipam.css

@@ -1223,3 +1223,125 @@ td.col-actions {
   color: var(--text-secondary);
   margin: 0;
 }
+
+/* ============================================================
+   HOST DETAIL — APPLICATIONS SECTION
+   ============================================================ */
+
+/* List of applications linked to a host (mirrors .port-list) */
+.app-list {
+  display: flex;
+  flex-direction: column;
+  margin-bottom: var(--size-md);
+  border-top: 1px solid var(--border);
+}
+
+.app-row {
+  display: flex;
+  align-items: center;
+  gap: var(--size-md);
+  padding: var(--size-sm) var(--size-xs);
+  border-bottom: 1px solid var(--border);
+}
+
+.app-row__name {
+  flex: 1;
+  font-size: var(--font-sm);
+}
+
+/* ── Pick list (scrollable, click to select) ── */
+.app-pick-list {
+  list-style: none;
+  margin: 0 0 var(--size-sm);
+  padding: 0;
+  max-height: 220px;
+  overflow-y: auto;
+  border: 1px solid var(--border);
+  border-radius: 6px;
+}
+
+.app-pick-item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: var(--size-sm) var(--size-md);
+  cursor: pointer;
+  font-size: var(--font-sm);
+  border-bottom: 1px solid var(--border);
+  transition: background 0.1s;
+}
+
+.app-pick-item:last-child {
+  border-bottom: none;
+}
+
+.app-pick-item:hover {
+  background: color-mix(in srgb, var(--accent) 10%, transparent);
+  color: var(--accent);
+}
+
+.app-pick-item__add {
+  font-size: 1.1rem;
+  font-weight: 600;
+  color: var(--accent);
+  opacity: 0.7;
+}
+
+.app-pick-item:hover .app-pick-item__add {
+  opacity: 1;
+}
+
+/* ── Selected tags (shown below the pick list) ── */
+.app-selected-section {
+  display: flex;
+  flex-direction: column;
+  gap: var(--size-xs);
+  padding-top: var(--size-sm);
+  border-top: 1px solid var(--border);
+  margin-top: var(--size-xs);
+}
+
+.app-selected-label {
+  font-size: var(--font-xs, 0.75rem);
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  color: var(--text-secondary);
+}
+
+.app-selected-list {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--size-xs);
+}
+
+.app-selected-tag {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  padding: 2px 8px 2px 10px;
+  border-radius: 999px;
+  background: color-mix(in srgb, var(--accent) 15%, transparent);
+  border: 1px solid color-mix(in srgb, var(--accent) 40%, transparent);
+  color: var(--accent);
+  font-size: var(--font-sm);
+  font-weight: 500;
+}
+
+.app-selected-tag__remove {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  background: none;
+  border: none;
+  padding: 0 2px;
+  cursor: pointer;
+  font-size: 0.9rem;
+  color: var(--accent);
+  opacity: 0.7;
+  line-height: 1;
+}
+
+.app-selected-tag__remove:hover {
+  opacity: 1;
+}