KERNlang · cukas · Jul 16, 2026 · Jul 16, 2026 · Jul 16, 2026
diff --git a/packages/cli/src/generated/surfaces/app-terminal.ts b/packages/cli/src/generated/surfaces/app-terminal.ts
@@ -45,33 +45,26 @@ export function normalizeTerminalMode(value: unknown): 'auto'|'native'|'fullscre
 }
 
 /**
- * Resolve auto terminal policy deterministically. Explicit modes win; auto avoids alternate-screen rendering where scrollback or terminal capability would be harmed.
+ * Resolve the terminal policy deterministically. Explicit modes win. Auto is NATIVE: the Static-sealed transcript lives in real terminal scrollback with the composer/status pinned at the bottom (the Claude-Code/Codex mix). Fullscreen (alternate screen) kills terminal scrollback, so it is strictly opt-in via `agon config terminalMode fullscreen` — never a default (regression 2026-07-16: auto→fullscreen shipped and broke scroll-up for every user).
  */
 // @kern-source: app-terminal:34
 export function resolveTerminalMode(value: unknown, env?: Record<string,string|undefined>, isTTY?: boolean): 'native'|'fullscreen' {
   const configured = normalizeTerminalMode(value);
   if (configured === 'native' || configured === 'fullscreen') return configured;
-  const runtimeEnv = env ?? process.env;
-  const runtimeIsTTY = isTTY ?? Boolean(process.stdout.isTTY);
-  const truthy = (raw: unknown) => ['1', 'true', 'yes', 'on'].includes(String(raw ?? '').trim().toLowerCase());
-  if (!runtimeIsTTY) return 'native';
-  if (truthy(runtimeEnv?.AGON_NO_ALT_SCREEN) || truthy(runtimeEnv?.CI)) return 'native';
-  if (String(runtimeEnv?.TERM ?? '').trim().toLowerCase() === 'dumb') return 'native';
-  if (String(runtimeEnv?.ZELLIJ ?? '').trim() || String(runtimeEnv?.ZELLIJ_SESSION_NAME ?? '').trim()) return 'native';
-  return 'fullscreen';
+  return 'native';
 }
 
 /**
  * Clamp a terminal resize into one atomic viewport value so width and height never render as mismatched frames.
  */
-// @kern-source: app-terminal:49
+// @kern-source: app-terminal:42
 export function normalizeTerminalSize(columns: unknown, rows: unknown): {width:number,height:number} {
   const width = Math.max(40, Math.floor(Number(columns) || 100));
   const height = Math.max(8, Math.floor(Number(rows) || 24));
   return { width, height };
 }
 
-// @kern-source: app-terminal:57
+// @kern-source: app-terminal:50
 export function fileRailWidthForTerminal(termWidth: number, expanded: boolean): number {
   const safeWidth = Math.max(40, Math.floor((Number(termWidth) || 100)));
   if (expanded) {
@@ -80,7 +73,7 @@ export function fileRailWidthForTerminal(termWidth: number, expanded: boolean):
   return Math.max(28, Math.min(42, Math.floor((safeWidth * 0.22))));
 }
 
-// @kern-source: app-terminal:64
+// @kern-source: app-terminal:57
 export function fileRailMaxRowsForTerminal(termHeight: number, terminalMode: string, expanded: boolean): number {
   const safeHeight = Math.max(8, Math.floor((Number(termHeight) || 24)));
   if (terminalMode === 'native') {
@@ -98,7 +91,7 @@ export function fileRailMaxRowsForTerminal(termHeight: number, terminalMode: str
 /**
  * Pure terminal replay harness: summarizes the layout-sensitive parts of the REPL for fixed viewport sizes so unit tests can catch native/fullscreen regressions without launching an interactive TTY.
  */
-// @kern-source: app-terminal:75
+// @kern-source: app-terminal:68
 export function buildTerminalReplaySnapshot(blocks: OutputBlock[], opts: any): {terminalMode:'native'|'fullscreen'; mode:string; termWidth:number; termHeight:number; visibleBudget:number; transcriptRowCount:number; staticBlockCount:number; liveBlockCount:number; fileRailWidth:number; fileRailRows:number; headerRows:number; lowerChromeRows:number} {
   const terminalMode = resolveTerminalMode(opts?.terminalMode, opts?.env ?? {}, opts?.isTTY ?? true);
   const mode = String(opts?.mode ?? 'chat');

diff --git a/packages/cli/src/kern/surfaces/app-terminal.kern b/packages/cli/src/kern/surfaces/app-terminal.kern
@@ -32,18 +32,11 @@ module name=AppTerminal
     >>>
 
   fn name=resolveTerminalMode params="value:unknown,env?:Record<string,string|undefined>,isTTY?:boolean" returns="'native'|'fullscreen'" export=true
-    doc "Resolve auto terminal policy deterministically. Explicit modes win; auto avoids alternate-screen rendering where scrollback or terminal capability would be harmed."
+    doc "Resolve the terminal policy deterministically. Explicit modes win. Auto is NATIVE: the Static-sealed transcript lives in real terminal scrollback with the composer/status pinned at the bottom (the Claude-Code/Codex mix). Fullscreen (alternate screen) kills terminal scrollback, so it is strictly opt-in via `agon config terminalMode fullscreen` — never a default (regression 2026-07-16: auto→fullscreen shipped and broke scroll-up for every user)."
     handler <<<
       const configured = normalizeTerminalMode(value);
       if (configured === 'native' || configured === 'fullscreen') return configured;
-      const runtimeEnv = env ?? process.env;
-      const runtimeIsTTY = isTTY ?? Boolean(process.stdout.isTTY);
-      const truthy = (raw: unknown) => ['1', 'true', 'yes', 'on'].includes(String(raw ?? '').trim().toLowerCase());
-      if (!runtimeIsTTY) return 'native';
-      if (truthy(runtimeEnv?.AGON_NO_ALT_SCREEN) || truthy(runtimeEnv?.CI)) return 'native';
-      if (String(runtimeEnv?.TERM ?? '').trim().toLowerCase() === 'dumb') return 'native';
-      if (String(runtimeEnv?.ZELLIJ ?? '').trim() || String(runtimeEnv?.ZELLIJ_SESSION_NAME ?? '').trim()) return 'native';
-      return 'fullscreen';
+      return 'native';
     >>>
 
   fn name=normalizeTerminalSize params="columns:unknown,rows:unknown" returns="{width:number,height:number}" export=true

diff --git a/packages/core/src/generated/sessions/companion-dispatch.ts b/packages/core/src/generated/sessions/companion-dispatch.ts
@@ -81,6 +81,7 @@ export async function companionDispatch(opts: {config:CompanionConfig, binaryPat
   let nextId = 1;
   const pending = new Map<number, { resolve: (v: any) => void; reject: (e: Error) => void; timer: NodeJS.Timeout }>();
   const agentMessages: string[] = [];
+  let lastAcpPushWasChunk = false;
   let turnCompleted: Record<string, unknown> | null = null;
   let turnError: Record<string, unknown> | null = null;
   let threadId: string | null = null;
@@ -244,16 +245,32 @@ export async function companionDispatch(opts: {config:CompanionConfig, binaryPat
       const item = (msg.params as any)?.item;
       if (item?.type === 'agentMessage') {
         agentMessages.push(item.text);
+        lastAcpPushWasChunk = false;
       }
       if (item?.type === 'enteredReviewMode') {
         agentMessages.push(item.review);
+        lastAcpPushWasChunk = false;
       }
     } else if (msg.method === 'session/update') {
       // ACP protocol notifications
       const update = (msg.params as any)?.update;
       if (update?.sessionUpdate === 'agent_message_chunk') {
+        // Chunks are token-level DELTAS of one agent message (kimi streams
+        // per-word) — concatenate consecutive chunks into a single entry.
+        // Pushing each delta separately rendered one word per '\n\n' paragraph.
         const text = update.content?.text ?? '';
-        if (text) agentMessages.push(text);
+        if (text) {
+          if (lastAcpPushWasChunk && agentMessages.length > 0) {
+            agentMessages[agentMessages.length - 1] += text;
+          } else {
+            agentMessages.push(text);
+          }
+          lastAcpPushWasChunk = true;
+        }
+      } else if (update?.sessionUpdate === 'tool_call') {
+        // A tool call ends the contiguous text run — the next chunk starts a
+        // new message (kept as a separate '\n\n'-joined paragraph block).
+        lastAcpPushWasChunk = false;
       }
     } else if (msg.method === 'error') {
       turnError = (msg.params as Record<string, unknown>);
@@ -364,8 +381,10 @@ export async function companionDispatch(opts: {config:CompanionConfig, binaryPat
         prompt: [{ type: 'text', text: opts.prompt }],
       }) as any;
 
-      // ACP returns text directly in the prompt response
-      if (promptResult?.text) agentMessages.push(promptResult.text);
+      // Some ACP servers return the text directly in the prompt response —
+      // but only as a fallback when nothing was streamed via
+      // agent_message_chunk, else the trailing text would duplicate.
+      if (promptResult?.text && agentMessages.length === 0) agentMessages.push(promptResult.text);
       turnCompleted = promptResult ?? {};
     } else {
       // JSONRPC protocol (Codex)

diff --git a/packages/core/src/generated/sessions/session-acp.ts b/packages/core/src/generated/sessions/session-acp.ts
@@ -38,6 +38,39 @@ export function createAcpSession(config: PersistentSessionConfig): PersistentSes
     });
   }
 
+  function toAcpMcpServers(servers: Array<Record<string, unknown>> | undefined): Array<Record<string, unknown>> {
+    // ACP spec wire shape: stdio servers carry env as EnvVariable[] ({name,value})
+    // and REQUIRE args/env arrays; http/sse servers carry headers the same way.
+    // Agon's internal shape uses Record<string,string> env — strict ACP agents
+    // (kimi) reject that with -32602 Invalid params, lenient ones ignored it.
+    const toPairs = (rec: unknown): Array<{ name: string; value: string }> =>
+      Object.entries((rec ?? {}) as Record<string, unknown>).map(([name, value]) => ({ name, value: String(value) }));
+    const out: Array<Record<string, unknown>> = [];
+    for (const s of (servers ?? []) as any[]) {
+      // A malformed entry (http-typed without url, or stdio without command)
+      // would emit a wire object with undefined required fields — the exact
+      // -32602 class this normalizer exists to prevent. Skip it instead.
+      if (s.url || s.type === 'http' || s.type === 'sse') {
+        if (!s.url) continue;
+        out.push({
+          type: s.type === 'sse' ? 'sse' : 'http',
+          name: s.name,
+          url: s.url,
+          headers: Array.isArray(s.headers) ? s.headers : toPairs(s.headers),
+        });
+        continue;
+      }
+      if (!s.command) continue;
+      out.push({
+        name: s.name,
+        command: s.command,
+        args: Array.isArray(s.args) ? s.args : [],
+        env: Array.isArray(s.env) ? s.env : toPairs(s.env),
+      });
+    }
+    return out;
+  }
+
   function killProc(): void {
     if (!proc) return;
     try {
@@ -248,7 +281,7 @@ export function createAcpSession(config: PersistentSessionConfig): PersistentSes
       // Create session (pass system prompt if available)
       const sessParams: Record<string, unknown> = {
         cwd: config.cwd,
-        mcpServers: config.mcpServers ?? [],
+        mcpServers: toAcpMcpServers(config.mcpServers),
       };
       if (config.systemPrompt) {
         sessParams.systemPrompt = config.systemPrompt;

diff --git a/packages/core/src/kern/sessions/companion-dispatch.kern b/packages/core/src/kern/sessions/companion-dispatch.kern
@@ -73,6 +73,7 @@ fn name=companionDispatch async=true params="opts:{config:CompanionConfig, binar
     let nextId = 1;
     const pending = new Map<number, { resolve: (v: any) => void; reject: (e: Error) => void; timer: NodeJS.Timeout }>();
     const agentMessages: string[] = [];
+    let lastAcpPushWasChunk = false;
     let turnCompleted: Record<string, unknown> | null = null;
     let turnError: Record<string, unknown> | null = null;
     let threadId: string | null = null;
@@ -236,16 +237,32 @@ fn name=companionDispatch async=true params="opts:{config:CompanionConfig, binar
         const item = (msg.params as any)?.item;
         if (item?.type === 'agentMessage') {
           agentMessages.push(item.text);
+          lastAcpPushWasChunk = false;
         }
         if (item?.type === 'enteredReviewMode') {
           agentMessages.push(item.review);
+          lastAcpPushWasChunk = false;
         }
       } else if (msg.method === 'session/update') {
         // ACP protocol notifications
         const update = (msg.params as any)?.update;
         if (update?.sessionUpdate === 'agent_message_chunk') {
+          // Chunks are token-level DELTAS of one agent message (kimi streams
+          // per-word) — concatenate consecutive chunks into a single entry.
+          // Pushing each delta separately rendered one word per '\n\n' paragraph.
           const text = update.content?.text ?? '';
-          if (text) agentMessages.push(text);
+          if (text) {
+            if (lastAcpPushWasChunk && agentMessages.length > 0) {
+              agentMessages[agentMessages.length - 1] += text;
+            } else {
+              agentMessages.push(text);
+            }
+            lastAcpPushWasChunk = true;
+          }
+        } else if (update?.sessionUpdate === 'tool_call') {
+          // A tool call ends the contiguous text run — the next chunk starts a
+          // new message (kept as a separate '\n\n'-joined paragraph block).
+          lastAcpPushWasChunk = false;
         }
       } else if (msg.method === 'error') {
         turnError = (msg.params as Record<string, unknown>);
@@ -356,8 +373,10 @@ fn name=companionDispatch async=true params="opts:{config:CompanionConfig, binar
           prompt: [{ type: 'text', text: opts.prompt }],
         }) as any;
 
-        // ACP returns text directly in the prompt response
-        if (promptResult?.text) agentMessages.push(promptResult.text);
+        // Some ACP servers return the text directly in the prompt response —
+        // but only as a fallback when nothing was streamed via
+        // agent_message_chunk, else the trailing text would duplicate.
+        if (promptResult?.text && agentMessages.length === 0) agentMessages.push(promptResult.text);
         turnCompleted = promptResult ?? {};
       } else {
         // JSONRPC protocol (Codex)

diff --git a/packages/core/src/kern/sessions/session-acp.kern b/packages/core/src/kern/sessions/session-acp.kern
@@ -31,6 +31,39 @@ fn name=createAcpSession params="config:PersistentSessionConfig" returns="Persis
       });
     }
 
+    function toAcpMcpServers(servers: Array<Record<string, unknown>> | undefined): Array<Record<string, unknown>> {
+      // ACP spec wire shape: stdio servers carry env as EnvVariable[] ({name,value})
+      // and REQUIRE args/env arrays; http/sse servers carry headers the same way.
+      // Agon's internal shape uses Record<string,string> env — strict ACP agents
+      // (kimi) reject that with -32602 Invalid params, lenient ones ignored it.
+      const toPairs = (rec: unknown): Array<{ name: string; value: string }> =>
+        Object.entries((rec ?? {}) as Record<string, unknown>).map(([name, value]) => ({ name, value: String(value) }));
+      const out: Array<Record<string, unknown>> = [];
+      for (const s of (servers ?? []) as any[]) {
+        // A malformed entry (http-typed without url, or stdio without command)
+        // would emit a wire object with undefined required fields — the exact
+        // -32602 class this normalizer exists to prevent. Skip it instead.
+        if (s.url || s.type === 'http' || s.type === 'sse') {
+          if (!s.url) continue;
+          out.push({
+            type: s.type === 'sse' ? 'sse' : 'http',
+            name: s.name,
+            url: s.url,
+            headers: Array.isArray(s.headers) ? s.headers : toPairs(s.headers),
+          });
+          continue;
+        }
+        if (!s.command) continue;
+        out.push({
+          name: s.name,
+          command: s.command,
+          args: Array.isArray(s.args) ? s.args : [],
+          env: Array.isArray(s.env) ? s.env : toPairs(s.env),
+        });
+      }
+      return out;
+    }
+
     function killProc(): void {
       if (!proc) return;
       try {
@@ -241,7 +274,7 @@ fn name=createAcpSession params="config:PersistentSessionConfig" returns="Persis
         // Create session (pass system prompt if available)
         const sessParams: Record<string, unknown> = {
           cwd: config.cwd,
-          mcpServers: config.mcpServers ?? [],
+          mcpServers: toAcpMcpServers(config.mcpServers),
         };
         if (config.systemPrompt) {
           sessParams.systemPrompt = config.systemPrompt;

diff --git a/tests/unit/app-scroll.test.ts b/tests/unit/app-scroll.test.ts
@@ -170,7 +170,10 @@ describe('app scroll helpers', () => {
     expect(normalizeTerminalMode('fullscreen')).toBe('fullscreen');
     expect(resolveTerminalMode('native', {}, true)).toBe('native');
     expect(resolveTerminalMode('fullscreen', { ZELLIJ: '1' }, false)).toBe('fullscreen');
-    expect(resolveTerminalMode('auto', {}, true)).toBe('fullscreen');
+    // Auto is NATIVE: real scrollback + pinned composer (the Codex/Claude-Code
+    // mix). Fullscreen is opt-in only — an auto→fullscreen default shipped once
+    // and broke scroll-up for every user (2026-07-16).
+    expect(resolveTerminalMode('auto', {}, true)).toBe('native');
     expect(resolveTerminalMode('auto', { ZELLIJ: '1' }, true)).toBe('native');
     expect(resolveTerminalMode('auto', { TERM: 'dumb' }, true)).toBe('native');
     expect(resolveTerminalMode('auto', { AGON_NO_ALT_SCREEN: '1' }, true)).toBe('native');
@@ -399,7 +402,9 @@ describe('app scroll helpers', () => {
     }] satisfies OutputBlock[];
     const sizes = [[120, 36], [48, 16], [90, 28], [40, 12]] as const;
     const frames = sizes.map(([termWidth, termHeight]) => buildTerminalReplaySnapshot(blocks, {
-      terminalMode: 'auto',
+      // Fullscreen is opt-in only (auto resolves to native) — this test
+      // exercises the fullscreen viewport budgets, so request it explicitly.
+      terminalMode: 'fullscreen',
       env: {},
       isTTY: true,
       mode: 'chat',

diff --git a/tests/unit/companion-dispatch.test.ts b/tests/unit/companion-dispatch.test.ts
@@ -44,4 +44,43 @@ describe('companionDispatch', () => {
     expect(result.stdout).toBe('ok');
     expect(Date.now() - startedAt).toBeLessThan(3000);
   });
+
+  it('concatenates token-level ACP agent_message_chunk deltas instead of one word per paragraph', async () => {
+    // Fake ACP server: answers initialize/session/new, then streams the agent
+    // message as per-word chunks (kimi style) with a tool_call in the middle,
+    // then resolves session/prompt.
+    const script = [
+      "const rl = require('node:readline').createInterface({ input: process.stdin });",
+      "const w = (o) => process.stdout.write(JSON.stringify(o) + '\\n');",
+      "const chunk = (text) => w({ jsonrpc: '2.0', method: 'session/update', params: { update: { sessionUpdate: 'agent_message_chunk', content: { type: 'text', text } } } });",
+      "rl.on('line', (line) => {",
+      "  const msg = JSON.parse(line);",
+      "  if (msg.method === 'initialize') w({ jsonrpc: '2.0', id: msg.id, result: { protocolVersion: 1 } });",
+      "  if (msg.method === 'session/new') w({ jsonrpc: '2.0', id: msg.id, result: { sessionId: 's1' } });",
+      "  if (msg.method === 'session/prompt') {",
+      "    chunk('I\\'ll'); chunk(' start'); chunk(' by');",
+      "    w({ jsonrpc: '2.0', method: 'session/update', params: { update: { sessionUpdate: 'tool_call', toolCallId: 't1', title: 'ls', status: 'completed' } } });",
+      "    chunk(' Done'); chunk('.');",
+      "    w({ jsonrpc: '2.0', id: msg.id, result: { stopReason: 'end_turn' } });",
+      "  }",
+      "});",
+    ].join('');
+
+    const result = await companionDispatch({
+      binaryPath: process.execPath,
+      config: {
+        protocol: 'acp',
+        serverCmd: ['-e', script],
+      },
+      prompt: 'hello',
+      cwd: process.cwd(),
+      timeout: 5,
+      mode: 'exec',
+    });
+
+    expect(result.exitCode).toBe(0);
+    // Chunks within a run concatenate verbatim; the tool_call splits the runs
+    // into two '\n\n'-joined paragraphs.
+    expect(result.stdout).toBe("I'll start by\n\n Done.");
+  });
 });