diff --git a/crates/application/src/agent/usecases.rs b/crates/application/src/agent/usecases.rs
index fc45422..a459701 100644
--- a/crates/application/src/agent/usecases.rs
+++ b/crates/application/src/agent/usecases.rs
@@ -361,8 +361,12 @@ impl SaveOpenCodeProviderProfile {
             provider = provider.with_custom(custom);
         }
 
-        let mut profile = input.profile;
-        profile.opencode_provider = Some(provider);
+        // Route through the builder (ticket #97): `with_opencode_provider` clears
+        // any stale `opencode` (llamacpp) carried by the input profile, so the
+        // persisted profile honours the mutual-exclusion invariant instead of
+        // keeping both backends — which previously forced a wrong llamacpp
+        // fallback even when the user chose a cloud provider.
+        let profile = input.profile.with_opencode_provider(provider);
 
         self.profile_store.save(&profile).await?;
         Ok(SaveOpenCodeProviderProfileOutput { profile })
diff --git a/crates/application/src/error.rs b/crates/application/src/error.rs
index 779851d..7fcdc09 100644
--- a/crates/application/src/error.rs
+++ b/crates/application/src/error.rs
@@ -134,6 +134,7 @@ impl From<StoreError> for AppError {
     fn from(e: StoreError) -> Self {
         match e {
             StoreError::NotFound => Self::NotFound("store item".to_owned()),
+            StoreError::Invalid(message) => Self::Invalid(message),
             other => Self::Store(other.to_string()),
         }
     }
diff --git a/crates/domain/src/ports.rs b/crates/domain/src/ports.rs
index b74e1c8..5cccfcd 100644
--- a/crates/domain/src/ports.rs
+++ b/crates/domain/src/ports.rs
@@ -796,6 +796,12 @@ pub enum StoreError {
     /// Underlying I/O error.
     #[error("store io failed: {0}")]
     Io(String),
+    /// A persisted item violated a domain invariant — surfaced by defense-in-depth
+    /// guards (e.g. [`crate::profile::AgentProfile::opencode_backend_is_consistent`],
+    /// ticket #97). Mapped upstream to an *invalid input* error (not a generic
+    /// store failure) so callers can distinguish invariant violations.
+    #[error("invalid persisted item: {0}")]
+    Invalid(String),
 }
 
 /// Errors from the [`MemoryStore`].
diff --git a/crates/domain/src/profile.rs b/crates/domain/src/profile.rs
index cde96e3..8c49285 100644
--- a/crates/domain/src/profile.rs
+++ b/crates/domain/src/profile.rs
@@ -1127,18 +1127,28 @@ impl AgentProfile {
         self
     }
 
-    /// Builder : fixe la configuration OpenCode process-backed.
+    /// Builder : fixe la configuration OpenCode process-backed (provider custom
+    /// `llamacpp`). Garantit l'invariant [`Self::opencode_backend_is_consistent`]
+    /// (ticket #97) : positionner le backend local évacue tout backend cloud
+    /// précédemment fixé — les deux configurent le même champ `opencode.json`
+    /// `provider`/`model` et n'ont aucun sens combinées. Dernier appel gagnant.
     #[must_use]
     pub fn with_opencode(mut self, config: OpenCodeConfig) -> Self {
         self.opencode = Some(config);
+        self.opencode_provider = None;
         self
     }
 
     /// Builder : fixe la configuration OpenCode **cloud** (provider BUILT-IN,
-    /// ticket #92, lot B1).
+    /// ticket #92, lot B1). Garantit l'invariant
+    /// [`Self::opencode_backend_is_consistent`] (ticket #97) : positionner le
+    /// backend cloud évacue tout backend local (`llamacpp`) précédemment fixé —
+    /// sans quoi le stale `opencode` forcerait un repli sur llamacpp au lieu du
+    /// provider cloud choisi par l'utilisateur. Dernier appel gagnant.
     #[must_use]
     pub fn with_opencode_provider(mut self, config: OpenCodeProviderConfig) -> Self {
         self.opencode_provider = Some(config);
+        self.opencode = None;
         self
     }
 
@@ -1474,13 +1484,47 @@ mod mcp_tests {
         let neither = profile_without_mcp().with_structured_adapter(StructuredAdapter::OpenCode);
         assert!(neither.opencode_backend_is_consistent());
 
-        let both = profile_without_mcp()
+        let mut both = profile_without_mcp()
             .with_structured_adapter(StructuredAdapter::OpenCode)
-            .with_opencode(local)
-            .with_opencode_provider(cloud);
+            .with_opencode(local.clone());
+        // The builders now enforce mutual exclusion (ticket #97), so an
+        // inconsistent profile is only reachable via direct mutation or a
+        // corrupted on-disk file — simulate that to exercise the predicate.
+        both.opencode_provider = Some(cloud.clone());
         assert!(!both.opencode_backend_is_consistent());
     }
 
+    #[test]
+    fn opencode_builders_enforce_mutual_exclusion_last_wins() {
+        let local = OpenCodeConfig::new(
+            "http://localhost:8080/v1",
+            None,
+            "qwen3-coder-30b",
+            None,
+            None,
+        )
+        .unwrap();
+        let cloud = OpenCodeProviderConfig::new("anthropic", "claude-sonnet-5", crate::ports::SecretRef::new("secret-cloud")).unwrap();
+
+        // Setting the cloud provider clears a previously-set local one.
+        let cloud_wins = profile_without_mcp()
+            .with_structured_adapter(StructuredAdapter::OpenCode)
+            .with_opencode(local.clone())
+            .with_opencode_provider(cloud.clone());
+        assert!(cloud_wins.opencode_backend_is_consistent());
+        assert!(cloud_wins.opencode.is_none(), "stale local backend dropped");
+        assert_eq!(cloud_wins.opencode_provider.as_ref().unwrap().provider_id, "anthropic");
+
+        // Setting the local provider clears a previously-set cloud one.
+        let local_wins = profile_without_mcp()
+            .with_structured_adapter(StructuredAdapter::OpenCode)
+            .with_opencode_provider(cloud)
+            .with_opencode(local);
+        assert!(local_wins.opencode_backend_is_consistent());
+        assert!(local_wins.opencode_provider.is_none(), "stale cloud backend dropped");
+        assert!(local_wins.opencode.is_some());
+    }
+
     #[test]
     fn opencode_provider_config_serialises_no_local_model_server_id_leak() {
         let config = OpenCodeProviderConfig::new("openrouter", "some-model", crate::ports::SecretRef::new("secret-openrouter")).unwrap();
diff --git a/crates/infrastructure/src/store/profile.rs b/crates/infrastructure/src/store/profile.rs
index 59f454a..77c2828 100644
--- a/crates/infrastructure/src/store/profile.rs
+++ b/crates/infrastructure/src/store/profile.rs
@@ -81,10 +81,23 @@ impl FsProfileStore {
     }
 
     /// Reads and parses the doc, returning an empty default if the file is absent.
+    ///
+    /// Runs a one-pass **repair** (ticket #97): a profile corrupted on disk may
+    /// carry both `opencode` (llamacpp) and `opencodeProvider` (cloud). The cloud
+    /// provider is the user's actual intent (the bug duplicated the local backend
+    /// even when a provider was chosen), so the stale `opencode` is dropped. This
+    /// makes the on-disk state converge with the now-enforced builder invariant.
     async fn read_doc(&self) -> Result<ProfilesDoc, StoreError> {
         match self.fs.read(&self.path()).await {
             Ok(bytes) => {
-                serde_json::from_slice(&bytes).map_err(|e| StoreError::Serialization(e.to_string()))
+                let mut doc: ProfilesDoc =
+                    serde_json::from_slice(&bytes).map_err(|e| StoreError::Serialization(e.to_string()))?;
+                for profile in &mut doc.profiles {
+                    if !profile.opencode_backend_is_consistent() {
+                        profile.opencode = None;
+                    }
+                }
+                Ok(doc)
             }
             Err(domain::ports::FsError::NotFound(_)) => Ok(ProfilesDoc::default()),
             Err(e) => Err(StoreError::Io(e.to_string())),
@@ -114,6 +127,16 @@ impl ProfileStore for FsProfileStore {
     }
 
     async fn save(&self, profile: &AgentProfile) -> Result<(), StoreError> {
+        // Defense-in-depth (ticket #97): refuse to persist a profile that violates
+        // the OpenCode backend mutual-exclusion invariant. The application layer
+        // now routes through the builders (which enforce exclusion), so this guard
+        // only ever fires for a future/buggy caller that mutates fields directly.
+        if !profile.opencode_backend_is_consistent() {
+            return Err(StoreError::Invalid(format!(
+                "profile `{}` carries both `opencode` and `opencodeProvider` (mutually exclusive)",
+                profile.name
+            )));
+        }
         let mut doc = self.read_doc().await?;
         if let Some(slot) = doc.profiles.iter_mut().find(|p| p.id == profile.id) {
             *slot = profile.clone();
diff --git a/crates/infrastructure/tests/profile_store.rs b/crates/infrastructure/tests/profile_store.rs
index ca462d6..e0c191e 100644
--- a/crates/infrastructure/tests/profile_store.rs
+++ b/crates/infrastructure/tests/profile_store.rs
@@ -6,8 +6,8 @@ use std::path::PathBuf;
 use std::sync::Arc;
 
 use domain::ids::ProfileId;
-use domain::ports::{FileSystem, ProfileStore, RemotePath, StoreError};
-use domain::profile::{AgentProfile, ContextInjection};
+use domain::ports::{FileSystem, ProfileStore, RemotePath, SecretRef, StoreError};
+use domain::profile::{AgentProfile, ContextInjection, OpenCodeConfig, OpenCodeProviderConfig, StructuredAdapter};
 use infrastructure::{FsProfileStore, LocalFileSystem};
 use uuid::Uuid;
 
@@ -168,3 +168,88 @@ async fn profiles_file_is_camelcase_versioned() {
     assert_eq!(entry["contextInjection"]["strategy"], "conventionFile");
     assert_eq!(entry["contextInjection"]["target"], "CLAUDE.md");
 }
+
+/// Fixture pair for ticket #97: the local llama.cpp backend (`opencode`) and the
+/// cloud provider (`opencodeProvider`) — the two mutually exclusive OpenCode
+/// backends. A profile carrying both is inconsistent.
+fn opencode_backends() -> (OpenCodeConfig, OpenCodeProviderConfig) {
+    let local =
+        OpenCodeConfig::new("http://localhost:8080/v1", None, "qwen3-coder-30b", None, None).unwrap();
+    let cloud =
+        OpenCodeProviderConfig::new("anthropic", "claude-sonnet-5", SecretRef::new("secret-cloud"))
+            .unwrap();
+    (local, cloud)
+}
+
+/// Ticket #97 — read repair (`read_doc`, profile.rs:90-105): a profile corrupted
+/// on disk (both `opencode` and `opencodeProvider` present) is silently repaired
+/// on read by dropping the stale `opencode`, converging with the enforced
+/// builder invariant. The cloud provider — the user's actual intent — is kept.
+#[tokio::test]
+async fn read_doc_repairs_stale_opencode_when_both_sections_present() {
+    let tmp = TempDir::new();
+    let (local, cloud) = opencode_backends();
+
+    // The `save` guard would refuse this, so plant the corruption directly on
+    // disk (bypassing the guard), exactly like a stale file from an older build.
+    let mut corrupted = sample(1, "OpenCode Cloud", "opencode")
+        .with_structured_adapter(StructuredAdapter::OpenCode)
+        .with_opencode(local);
+    corrupted.opencode_provider = Some(cloud.clone());
+    assert!(
+        !corrupted.opencode_backend_is_consistent(),
+        "fixture must violate the invariant"
+    );
+
+    let fs = LocalFileSystem::new();
+    let doc = serde_json::json!({ "version": 1, "profiles": [corrupted] });
+    fs.write(&tmp.child("profiles.json"), &serde_json::to_vec_pretty(&doc).unwrap())
+        .await
+        .unwrap();
+
+    let store = store(&tmp);
+    let listed = store.list().await.expect("read repairs instead of failing");
+    assert_eq!(listed.len(), 1, "corrupted profile preserved as an entry");
+    let repaired = &listed[0];
+    assert!(repaired.opencode.is_none(), "stale local `opencode` dropped on read");
+    assert_eq!(
+        repaired.opencode_provider.as_ref().unwrap().provider_id,
+        "anthropic",
+        "cloud `opencodeProvider` preserved"
+    );
+    assert!(
+        repaired.opencode_backend_is_consistent(),
+        "read repair restored the mutual-exclusion invariant"
+    );
+}
+
+/// Ticket #97 — write guard (`save`, profile.rs:129-139): persisting a profile
+/// that violates the OpenCode backend mutual-exclusion invariant is rejected
+/// with [`StoreError::Invalid`], and nothing is written to disk.
+#[tokio::test]
+async fn save_rejects_profile_violating_backend_exclusion() {
+    let tmp = TempDir::new();
+    let store = store(&tmp);
+    let (local, cloud) = opencode_backends();
+
+    // Only reachable via direct mutation: the builders enforce exclusion
+    // (last-wins), so an inconsistent profile cannot be built through the API.
+    let mut inconsistent = sample(1, "OpenCode Both", "opencode")
+        .with_structured_adapter(StructuredAdapter::OpenCode)
+        .with_opencode(local);
+    inconsistent.opencode_provider = Some(cloud);
+    assert!(!inconsistent.opencode_backend_is_consistent());
+
+    let err = store
+        .save(&inconsistent)
+        .await
+        .expect_err("save must reject an invariant-violating profile");
+    assert!(
+        matches!(err, StoreError::Invalid(_)),
+        "defense-in-depth guard maps to Invalid; got {err:?}"
+    );
+    assert!(
+        !store.is_configured().await.unwrap(),
+        "rejected save must not materialise profiles.json"
+    );
+}