diff --git a/packages/ui/src/stores/session-actions.ts b/packages/ui/src/stores/session-actions.ts
index 3cdf0321..af7515f8 100644
--- a/packages/ui/src/stores/session-actions.ts
+++ b/packages/ui/src/stores/session-actions.ts
@@ -11,6 +11,15 @@ import { removeMessagePartV2, removeMessageV2 } from "./message-v2/bridge"
 import { getLogger } from "../lib/logger"
 import { requestData } from "../lib/opencode-api"
 import { clearConversationPlaybackForSession } from "./conversation-speech"
+import {
+  getOverride,
+  setAgentOverride,
+  setModelOverride,
+  clearOverrides,
+  clearAgentOverride,
+  clearModelOverride,
+  getModelOverrideValue,
+} from "./session-overrides"
 
 const log = getLogger("actions")
 
@@ -183,20 +192,25 @@ async function sendMessage(
     /* trigger reactivity for legacy session data */
   })
 
+  // Only send agent/model when the user explicitly selected them (override state).
+  // session.agent/session.model are display state (what the server has), NOT user intent.
+  const userOverride = getOverride(instanceId, sessionId)
+  const overrideModel = userOverride?.model
+    ? getModelOverrideValue(instanceId, sessionId)
+    : undefined
+
   const requestBody = {
     parts: requestParts,
-    ...(session.agent && { agent: session.agent }),
-    ...(session.model.providerId &&
-      session.model.modelId && {
-        model: {
-          providerID: session.model.providerId,
-          modelID: session.model.modelId,
-        },
-      }),
-    ...(session.model.providerId &&
-      session.model.modelId &&
+    ...(userOverride?.agent && { agent: userOverride.agent }),
+    ...(overrideModel && {
+      model: {
+        providerID: overrideModel.providerId,
+        modelID: overrideModel.modelId,
+      },
+    }),
+    ...(overrideModel &&
       (() => {
-        const variant = getThinkingVariantToSend(instanceId, session.model)
+        const variant = getThinkingVariantToSend(instanceId, overrideModel)
         return variant ? { variant } : {}
       })()),
   }
@@ -216,6 +230,7 @@ async function sendMessage(
       }),
       "session.promptAsync",
     )
+    clearOverrides(instanceId, sessionId)
   } catch (error) {
     log.error("Failed to send prompt", error)
     throw error
@@ -254,14 +269,20 @@ async function executeCustomCommand(
     messageID: createId("msg"),
   }
 
-  if (session.agent) {
-    body.agent = session.agent
+  // Only send agent/model when the user explicitly selected them (override state).
+  const userOverride = getOverride(instanceId, sessionId)
+
+  if (userOverride?.agent) {
+    body.agent = userOverride.agent
   }
 
-  if (session.model.providerId && session.model.modelId) {
-    body.model = `${session.model.providerId}/${session.model.modelId}`
-    const variant = getThinkingVariantToSend(instanceId, session.model)
-    if (variant) body.variant = variant
+  if (userOverride?.model) {
+    const overrideModel = getModelOverrideValue(instanceId, sessionId)
+    if (overrideModel) {
+      body.model = `${overrideModel.providerId}/${overrideModel.modelId}`
+      const variant = getThinkingVariantToSend(instanceId, overrideModel)
+      if (variant) body.variant = variant
+    }
   }
 
   await requestData(
@@ -271,6 +292,7 @@ async function executeCustomCommand(
     }),
     "session.command",
   )
+  clearOverrides(instanceId, sessionId)
 }
 
 async function runShellCommand(instanceId: string, sessionId: string, command: string): Promise<void> {
@@ -287,7 +309,9 @@ async function runShellCommand(instanceId: string, sessionId: string, command: s
     throw new Error("Session not found")
   }
 
-  const agent = session.agent || "build"
+  // Only use override agent — fall back to "build" (OpenCode default) if user hasn't explicitly set one.
+  const userOverride = getOverride(instanceId, sessionId)
+  const agent = userOverride?.agent || "build"
 
   await requestData(
     client.session.shell({
@@ -297,6 +321,9 @@ async function runShellCommand(instanceId: string, sessionId: string, command: s
     }),
     "session.shell",
   )
+  if (userOverride?.agent) {
+    clearAgentOverride(instanceId, sessionId)
+  }
 }
 
 async function abortSession(instanceId: string, sessionId: string): Promise<void> {
@@ -335,6 +362,7 @@ async function updateSessionAgent(instanceId: string, sessionId: string, agent:
   const nextModel = await getDefaultModel(instanceId, agent)
   const shouldApplyModel = isModelValid(instanceId, nextModel)
 
+  // Update local display state
   withSession(instanceId, sessionId, (current) => {
     current.agent = agent
     if (shouldApplyModel) {
@@ -342,6 +370,15 @@ async function updateSessionAgent(instanceId: string, sessionId: string, agent:
     }
   })
 
+  // Record explicit user override so the next prompt sends these values.
+  setAgentOverride(instanceId, sessionId, agent)
+  if (shouldApplyModel) {
+    setModelOverride(instanceId, sessionId, nextModel)
+  } else {
+    // Agent changed but no valid model found — clear any stale model override
+    clearModelOverride(instanceId, sessionId)
+  }
+
   if (agent && shouldApplyModel) {
     await setAgentModelPreference(instanceId, agent, nextModel)
   }
@@ -367,10 +404,14 @@ async function updateSessionModel(
     return
   }
 
+  // Update local display state
   withSession(instanceId, sessionId, (current) => {
     current.model = model
   })
 
+  // Record explicit user override so the next prompt sends this model.
+  setModelOverride(instanceId, sessionId, model)
+
   if (session.agent) {
     await setAgentModelPreference(instanceId, session.agent, model)
   }
diff --git a/packages/ui/src/stores/session-api.ts b/packages/ui/src/stores/session-api.ts
index 36609380..057c52a7 100644
--- a/packages/ui/src/stores/session-api.ts
+++ b/packages/ui/src/stores/session-api.ts
@@ -49,6 +49,11 @@ import {
   removeParentSessionMapping,
   setWorktreeSlugForParentSession,
 } from "./worktrees"
+import {
+  clearOverrides,
+  setAgentOverride,
+  setModelOverride,
+} from "./session-overrides"
 
 const log = getLogger("api")
 
@@ -443,6 +448,16 @@ async function createSession(instanceId: string, agent?: string): Promise<Sessio
       log.warn("Failed to persist session worktree mapping", { instanceId, sessionId: session.id, worktreeSlug, error })
     })
 
+    // Record the initial agent/model as explicit user overrides so the first
+    // prompt sends them.  After a prompt/command consumes them or messages are
+    // reloaded from the server, the overrides are cleared automatically.
+    if (selectedAgent) {
+      setAgentOverride(instanceId, session.id, selectedAgent)
+    }
+    if (isModelValid(instanceId, defaultModel)) {
+      setModelOverride(instanceId, session.id, defaultModel)
+    }
+
     return session
   } catch (error) {
     log.error("Failed to create session:", error)
@@ -851,6 +866,12 @@ async function loadMessages(
       return next
     })
 
+    // Server provided authoritative agent/model — clear pending user overrides
+    // so we don't resend stale selections on the next prompt.
+    if (agentName || (providerID && modelID)) {
+      clearOverrides(instanceId, sessionId)
+    }
+
     setMessagesLoaded((prev) => {
       const next = new Map(prev)
       const loadedSet = next.get(instanceId) || new Set()
diff --git a/packages/ui/src/stores/session-overrides.ts b/packages/ui/src/stores/session-overrides.ts
new file mode 100644
index 00000000..487b4a6c
--- /dev/null
+++ b/packages/ui/src/stores/session-overrides.ts
@@ -0,0 +1,132 @@
+/**
+ * Session overrides track user-explicit agent/model selections.
+ *
+ * Invariant:
+ *   `session.agent` / `session.model` = display state (what the client believes the server has).
+ *   `overrides.agent` / `overrides.model` = user intent (what the user wants to force on the next request).
+ *
+ * Only overrides are sent in promptAsync / command request bodies.
+ * Server-observed values (from SSE, message loading) update display state but do NOT create overrides.
+ */
+
+import { createSignal } from "solid-js"
+
+export interface SessionOverride {
+  agent?: string
+  /** Format: "providerId/modelId" */
+  model?: string
+}
+
+type OverrideMap = Map<string, Map<string, SessionOverride>>
+
+const [overrides, setOverrides] = createSignal<OverrideMap>(new Map())
+
+function getOverride(instanceId: string, sessionId: string): SessionOverride | undefined {
+  return overrides().get(instanceId)?.get(sessionId)
+}
+
+function setOverride(instanceId: string, sessionId: string, patch: Partial<SessionOverride>): void {
+  setOverrides((prev) => {
+    const next = new Map(prev)
+    const instanceMap = new Map(next.get(instanceId) ?? new Map<string, SessionOverride>())
+    const existing = instanceMap.get(sessionId) ?? {}
+    const merged: SessionOverride = { ...existing, ...patch }
+
+    // Clean up undefined/empty values
+    if (!merged.agent) delete merged.agent
+    if (!merged.model) delete merged.model
+
+    if (!merged.agent && !merged.model) {
+      instanceMap.delete(sessionId)
+    } else {
+      instanceMap.set(sessionId, merged)
+    }
+
+    if (instanceMap.size === 0) {
+      next.delete(instanceId)
+    } else {
+      next.set(instanceId, instanceMap)
+    }
+    return next
+  })
+}
+
+/** Record that the user explicitly selected an agent for this session. */
+function setAgentOverride(instanceId: string, sessionId: string, agent: string): void {
+  setOverride(instanceId, sessionId, { agent })
+}
+
+/** Record that the user explicitly selected a model for this session. */
+function setModelOverride(instanceId: string, sessionId: string, model: { providerId: string; modelId: string }): void {
+  if (!model.providerId || !model.modelId) return
+  setOverride(instanceId, sessionId, { model: `${model.providerId}/${model.modelId}` })
+}
+
+/** Clear the agent override (e.g., after server confirms the agent change). */
+function clearAgentOverride(instanceId: string, sessionId: string): void {
+  const current = getOverride(instanceId, sessionId)
+  if (!current?.agent) return
+  setOverride(instanceId, sessionId, { agent: undefined })
+}
+
+/** Clear the model override (e.g., after server confirms the model change). */
+function clearModelOverride(instanceId: string, sessionId: string): void {
+  const current = getOverride(instanceId, sessionId)
+  if (!current?.model) return
+  setOverride(instanceId, sessionId, { model: undefined })
+}
+
+/** Clear both overrides for a session (e.g., when server state diverges). */
+function clearOverrides(instanceId: string, sessionId: string): void {
+  setOverrides((prev) => {
+    const next = new Map(prev)
+    const instanceMap = next.get(instanceId)
+    if (!instanceMap) return prev
+    if (!instanceMap.has(sessionId)) return prev
+    const updated = new Map(instanceMap)
+    updated.delete(sessionId)
+    if (updated.size === 0) {
+      next.delete(instanceId)
+    } else {
+      next.set(instanceId, updated)
+    }
+    return next
+  })
+}
+
+/** Clear all overrides for an instance (e.g., on disconnect). */
+function clearInstanceOverrides(instanceId: string): void {
+  setOverrides((prev) => {
+    if (!prev.has(instanceId)) return prev
+    const next = new Map(prev)
+    next.delete(instanceId)
+    return next
+  })
+}
+
+/**
+ * Parse a model override string back into providerId/modelId.
+ * Returns undefined if no model override exists.
+ */
+function getModelOverrideValue(instanceId: string, sessionId: string): { providerId: string; modelId: string } | undefined {
+  const raw = getOverride(instanceId, sessionId)?.model
+  if (!raw) return undefined
+  const slashIndex = raw.indexOf("/")
+  if (slashIndex <= 0) return undefined
+  return {
+    providerId: raw.substring(0, slashIndex),
+    modelId: raw.substring(slashIndex + 1),
+  }
+}
+
+export {
+  overrides,
+  getOverride,
+  setAgentOverride,
+  setModelOverride,
+  clearAgentOverride,
+  clearModelOverride,
+  clearOverrides,
+  clearInstanceOverrides,
+  getModelOverrideValue,
+}