feat(provider-adapter): implement multi-provider abstraction layer (Phase 1)

Add provider types, registry, capabilities, and message adapter registry.
Rename sdk-messages→claude-messages, agent-runner→claude-runner,
ClaudeSession→AgentSession. Update Rust AgentQueryOptions with provider
and provider_config fields. Capability-driven AgentPane rendering.

v2/src/lib/components/Agent/AgentPane.svelte

@@ -21,7 +21,8 @@
     CostContent,
     ErrorContent,
     StatusContent,
-  } from '../../adapters/sdk-messages';
+  } from '../../adapters/claude-messages';
+  import type { ProviderId, ProviderCapabilities } from '../../providers/types';
 
   // Tool-aware truncation limits
   const MAX_BASH_LINES = 500;
@@ -29,15 +30,28 @@
   const MAX_GLOB_LINES = 20;
   const MAX_DEFAULT_LINES = 30;
 
+  // Default capabilities (Claude — all enabled)
+  const DEFAULT_CAPABILITIES: ProviderCapabilities = {
+    hasProfiles: true,
+    hasSkills: true,
+    hasModelSelection: true,
+    hasSandbox: false,
+    supportsSubagents: true,
+    supportsCost: true,
+    supportsResume: true,
+  };
+
   interface Props {
     sessionId: string;
     prompt?: string;
     cwd?: string;
     profile?: string;
+    provider?: ProviderId;
+    capabilities?: ProviderCapabilities;
     onExit?: () => void;
   }
 
-  let { sessionId, prompt: initialPrompt = '', cwd: initialCwd, profile: profileName, onExit }: Props = $props();
+  let { sessionId, prompt: initialPrompt = '', cwd: initialCwd, profile: profileName, provider: providerId = 'claude', capabilities = DEFAULT_CAPABILITIES, onExit }: Props = $props();
 
   let session = $derived(getAgentSession(sessionId));
   let inputPrompt = $state(initialPrompt);
@@ -106,9 +120,10 @@
 
   onMount(async () => {
     await getHighlighter();
+    // Only load profiles/skills for providers that support them
     const [profileList, skillList] = await Promise.all([
-      listProfiles().catch(() => []),
-      listSkills().catch(() => []),
+      capabilities.hasProfiles ? listProfiles().catch(() => []) : Promise.resolve([]),
+      capabilities.hasSkills ? listSkills().catch(() => []) : Promise.resolve([]),
     ]);
     profiles = profileList;
     skills = skillList;
@@ -144,6 +159,7 @@
 
     const profile = profileName ? profiles.find(p => p.name === profileName) : undefined;
     await queryAgent({
+      provider: providerId,
       session_id: sessionId,
       prompt: text,
       cwd: initialCwd || undefined,
@@ -335,7 +351,7 @@
           {#if msg.type === 'init'}
             <div class="msg-init">
               <span class="label">Session started</span>
-              <span class="model">{(msg.content as import('../../adapters/sdk-messages').InitContent).model}</span>
+              <span class="model">{(msg.content as import('../../adapters/claude-messages').InitContent).model}</span>
             </div>
           {:else if msg.type === 'text'}
             {@const textContent = (msg.content as TextContent).text}
@@ -490,19 +506,21 @@
         </svg>
         New Session
       </button>
-      <button class="session-btn session-btn-continue" onclick={() => promptRef?.focus()}>
-        <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
-          <polyline points="9 18 15 12 9 6"></polyline>
-        </svg>
-        Continue
-      </button>
+      {#if capabilities.supportsResume}
+        <button class="session-btn session-btn-continue" onclick={() => promptRef?.focus()}>
+          <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+            <polyline points="9 18 15 12 9 6"></polyline>
+          </svg>
+          Continue
+        </button>
+      {/if}
     </div>
   {/if}
 
   <!-- Unified prompt input -->
   <div class="prompt-container" class:disabled={isRunning}>
     <div class="prompt-wrapper">
-      {#if showSkillMenu && filteredSkills.length > 0}
+      {#if capabilities.hasSkills && showSkillMenu && filteredSkills.length > 0}
         <div class="skill-menu">
           {#each filteredSkills as skill, i (skill.name)}
             <button

v2/src/lib/components/Terminal/AgentPreviewPane.svelte

@@ -13,7 +13,7 @@
     ErrorContent,
     TextContent,
     AgentMessage,
-  } from '../../adapters/sdk-messages';
+  } from '../../adapters/claude-messages';
   import '@xterm/xterm/css/xterm.css';
 
   interface Props {

v2/src/lib/components/Workspace/AgentSession.svelte

@@ -16,7 +16,8 @@
     setAgentSdkSessionId,
     getAgentSession,
   } from '../../stores/agents.svelte';
-  import type { AgentMessage } from '../../adapters/sdk-messages';
+  import type { AgentMessage } from '../../adapters/claude-messages';
+  import { getProvider, getDefaultProviderId } from '../../providers/registry.svelte';
   import AgentPane from '../Agent/AgentPane.svelte';
 
   interface Props {
@@ -26,6 +27,9 @@
 
   let { project, onsessionid }: Props = $props();
 
+  let providerId = $derived(project.provider ?? getDefaultProviderId());
+  let providerMeta = $derived(getProvider(providerId));
+
   let sessionId = $state(crypto.randomUUID());
   let lastState = $state<ProjectAgentState | null>(null);
   let loading = $state(true);
@@ -35,7 +39,7 @@
     sessionId = crypto.randomUUID();
     hasRestoredHistory = false;
     lastState = null;
-    registerSessionProject(sessionId, project.id);
+    registerSessionProject(sessionId, project.id, providerId);
     trackProject(project.id, sessionId);
     onsessionid?.(sessionId);
   }
@@ -70,7 +74,7 @@
     } finally {
       loading = false;
       // Register session -> project mapping for persistence + health tracking
-      registerSessionProject(sessionId, project.id);
+      registerSessionProject(sessionId, project.id, providerId);
       trackProject(project.id, sessionId);
       onsessionid?.(sessionId);
     }
@@ -112,7 +116,7 @@
   }
 </script>
 
-<div class="claude-session">
+<div class="agent-session">
   {#if loading}
     <div class="loading-state">Loading session...</div>
   {:else}
@@ -120,13 +124,15 @@
       {sessionId}
       cwd={project.cwd}
       profile={project.profile || undefined}
+      provider={providerId}
+      capabilities={providerMeta?.capabilities}
       onExit={handleNewSession}
     />
   {/if}
 </div>
 
 <style>
-  .claude-session {
+  .agent-session {
     height: 100%;
     overflow: hidden;
     display: flex;

v2/src/lib/components/Workspace/ContextTab.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import { getAgentSession, getTotalCost, type AgentSession } from '../../stores/agents.svelte';
-  import type { AgentMessage, ToolCallContent, CostContent, CompactionContent } from '../../adapters/sdk-messages';
+  import type { AgentMessage, ToolCallContent, CostContent, CompactionContent } from '../../adapters/claude-messages';
   import { extractFilePaths } from '../../utils/tool-files';
 
   interface Props {

v2/src/lib/components/Workspace/ProjectBox.svelte

@@ -3,7 +3,7 @@
   import type { ProjectConfig } from '../../types/groups';
   import { PROJECT_ACCENTS } from '../../types/groups';
   import ProjectHeader from './ProjectHeader.svelte';
-  import ClaudeSession from './ClaudeSession.svelte';
+  import AgentSession from './AgentSession.svelte';
   import TerminalTabs from './TerminalTabs.svelte';
   import TeamAgentsPanel from './TeamAgentsPanel.svelte';
   import ProjectFiles from './ProjectFiles.svelte';
@@ -148,7 +148,7 @@
   <div class="project-content-area">
     <!-- PERSISTED-EAGER: always mounted, toggled via display -->
     <div class="content-pane" style:display={activeTab === 'model' ? 'flex' : 'none'}>
-      <ClaudeSession {project} onsessionid={(id) => mainSessionId = id} />
+      <AgentSession {project} onsessionid={(id) => mainSessionId = id} />
       {#if mainSessionId}
         <TeamAgentsPanel {mainSessionId} />
       {/if}