COD-80 centralize terminal history/scrollback/buffer limits into config

Introduce src/config/terminal-history.ts: one place for terminal scrollback,
tmux history-limit, and PTY buffer byte caps, each overridable via env var or
the settings object and bounds-clamped via resolveTerminalHistoryConfig().
Defaults match the prior hardcoded values, so this is behavior-neutral. Wires
the resolver through buffer-limits, tmux-manager (incl. a setHistoryLimit so a
settings change applies live), session, server, system-routes, session-routes,
schemas, and the config port. Adds 4 optional settings keys (terminalScrollback
Lines, tmuxHistoryLimit, terminalBufferMaxBytes, terminalBufferTrimBytes) with
bounds + a trim<=max cross-check.

src/web/ports/config-port.ts

@@ -5,6 +5,7 @@
 
 import type { ClaudeMode, NiceConfig } from '../../types.js';
 import type { StateStore } from '../../state-store.js';
+import type { TerminalHistoryConfig } from '../../config/terminal-history.js';
 
 export interface ConfigPort {
   readonly store: StateStore;
@@ -15,6 +16,7 @@ export interface ConfigPort {
   getGlobalNiceConfig(): Promise<NiceConfig | undefined>;
   getModelConfig(): Promise<{ defaultModel?: string; agentTypeOverrides?: Record<string, string> } | null>;
   getClaudeModeConfig(): Promise<{ claudeMode?: ClaudeMode; allowedTools?: string }>;
+  getTerminalHistoryConfig(): Promise<TerminalHistoryConfig>;
   getDefaultClaudeMdPath(): Promise<string | undefined>;
   getLightState(): unknown;
   getLightSessionsState(): unknown[];

src/web/routes/session-routes.ts

@@ -406,6 +406,7 @@ export function registerSessionRoutes(
               ? modelConfig?.defaultModel || undefined
               : undefined;
     const claudeModeConfig = await ctx.getClaudeModeConfig();
+    const terminalHistoryConfig = await ctx.getTerminalHistoryConfig();
     const session = new Session({
       workingDir,
       mode,
@@ -422,6 +423,7 @@ export function registerSessionRoutes(
       resumeSessionId: validatedResumeId,
       envOverrides: body.envOverrides,
       effort: body.effort,
+      tmuxHistoryLimit: terminalHistoryConfig.tmuxHistoryLimit,
     });
 
     ctx.addSession(session);
@@ -1362,6 +1364,7 @@ export function registerSessionRoutes(
               ? qsModelConfig?.defaultModel || undefined
               : undefined;
     const qsClaudeModeConfig = await ctx.getClaudeModeConfig();
+    const qsTerminalHistoryConfig = await ctx.getTerminalHistoryConfig();
     const session = new Session({
       workingDir: casePath,
       mux: ctx.mux,
@@ -1376,6 +1379,7 @@ export function registerSessionRoutes(
       geminiConfig: mode === 'gemini' ? geminiConfig : undefined,
       envOverrides,
       effort,
+      tmuxHistoryLimit: qsTerminalHistoryConfig.tmuxHistoryLimit,
     });
 
     // Auto-detect completion phrase from CLAUDE.md BEFORE broadcasting

src/web/routes/system-routes.ts

@@ -49,6 +49,7 @@ import type { SessionPort, EventPort, ConfigPort, InfraPort, AuthPort } from '..
 import { AUTH_COOKIE_NAME } from '../middleware/auth.js';
 import { QR_AUTH_FAILURE_MAX } from '../../config/tunnel-config.js';
 import { AUTH_SESSION_TTL_MS } from '../../config/auth-config.js';
+import { resolveTerminalHistoryConfig } from '../../config/terminal-history.js';
 
 // Maximum screenshot upload size (10MB)
 const MAX_SCREENSHOT_SIZE = 10 * 1024 * 1024;
@@ -624,6 +625,11 @@ export function registerSystemRoutes(
       const merged = { ...existing, ...settingsToStore };
       await fs.writeFile(SETTINGS_PATH, JSON.stringify(merged, null, 2));
 
+      // Apply a changed tmux history-limit to all live sessions immediately.
+      if (settings.tmuxHistoryLimit !== undefined) {
+        await ctx.mux.setHistoryLimit(resolveTerminalHistoryConfig(merged).tmuxHistoryLimit);
+      }
+
       // Handle subagent tracking toggle dynamically
       toggleService((settings.subagentTrackingEnabled as boolean) ?? true, subagentWatcher, 'Subagent watcher');
 

src/web/schemas.ts

@@ -9,6 +9,12 @@
 
 import { z } from 'zod';
 import { SAFE_PATH_PATTERN, isSafePushEndpoint } from '../utils/index.js';
+import {
+  MAX_TERMINAL_BUFFER_BYTES,
+  MAX_TERMINAL_SCROLLBACK_LINES,
+  MIN_TERMINAL_BUFFER_BYTES,
+  MIN_TERMINAL_SCROLLBACK_LINES,
+} from '../config/terminal-history.js';
 
 // ========== Path Validation ==========
 
@@ -412,6 +418,16 @@ export const SettingsUpdateSchema = z
     allowedTools: z.string().max(2000).optional(),
     // Codex CLI settings
     codexDangerouslyBypassApprovals: z.boolean().optional(),
+    // Terminal history and retention
+    terminalScrollbackLines: z
+      .number()
+      .int()
+      .min(MIN_TERMINAL_SCROLLBACK_LINES)
+      .max(MAX_TERMINAL_SCROLLBACK_LINES)
+      .optional(),
+    tmuxHistoryLimit: z.number().int().min(MIN_TERMINAL_SCROLLBACK_LINES).max(MAX_TERMINAL_SCROLLBACK_LINES).optional(),
+    terminalBufferMaxBytes: z.number().int().min(MIN_TERMINAL_BUFFER_BYTES).max(MAX_TERMINAL_BUFFER_BYTES).optional(),
+    terminalBufferTrimBytes: z.number().int().min(MIN_TERMINAL_BUFFER_BYTES).max(MAX_TERMINAL_BUFFER_BYTES).optional(),
     // CPU priority
     nice: z
       .object({
@@ -480,7 +496,20 @@ export const SettingsUpdateSchema = z
       .max(20)
       .optional(),
   })
-  .strict();
+  .strict()
+  .superRefine((settings, ctx) => {
+    if (
+      settings.terminalBufferMaxBytes !== undefined &&
+      settings.terminalBufferTrimBytes !== undefined &&
+      settings.terminalBufferTrimBytes > settings.terminalBufferMaxBytes
+    ) {
+      ctx.addIssue({
+        code: z.ZodIssueCode.custom,
+        path: ['terminalBufferTrimBytes'],
+        message: 'terminalBufferTrimBytes must be less than or equal to terminalBufferMaxBytes',
+      });
+    }
+  });
 
 /**
  * Schema for POST /api/sessions/:id/input with length limit

src/web/server.ts

@@ -129,6 +129,7 @@ import {
 import type { EventLoopMonitorHandle } from '../utils/index.js';
 import { MAX_CONCURRENT_SESSIONS, MAX_SSE_CLIENTS } from '../config/map-limits.js';
 import { MAX_PASTE_IMAGE_BYTES } from '../config/buffer-limits.js';
+import { resolveTerminalHistoryConfig } from '../config/terminal-history.js';
 import { SseEvent } from './sse-events.js';
 import { getLatestPlanUsage } from './plan-usage-latest.js';
 import type { ScheduledRun } from './ports/index.js';
@@ -587,6 +588,7 @@ export class WebServer extends EventEmitter {
       getGlobalNiceConfig: this.getGlobalNiceConfig.bind(this),
       getModelConfig: this.getModelConfig.bind(this),
       getClaudeModeConfig: this.getClaudeModeConfig.bind(this),
+      getTerminalHistoryConfig: this.getTerminalHistoryConfig.bind(this),
       getDefaultClaudeMdPath: this.getDefaultClaudeMdPath.bind(this),
       getLightState: this.getLightState.bind(this),
       getLightSessionsState: this.getLightSessionsState.bind(this),
@@ -1463,6 +1465,12 @@ export class WebServer extends EventEmitter {
     return {};
   }
 
+  // Resolve the bounds-clamped terminal-history config from settings.json.
+  private async getTerminalHistoryConfig() {
+    const settings = await this.readSettings();
+    return resolveTerminalHistoryConfig(settings);
+  }
+
   // Helper to get model configuration from settings
   private async getModelConfig(): Promise<{
     defaultModel?: string;