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/tmux-manager.ts

@@ -65,6 +65,7 @@ import type {
 // ============================================================================
 
 import { EXEC_TIMEOUT_MS } from './config/exec-timeout.js';
+import { DEFAULT_TMUX_HISTORY_LIMIT } from './config/terminal-history.js';
 
 /** Delay after tmux session creation — enough for detached tmux to be queryable */
 const TMUX_CREATION_WAIT_MS = 100;
@@ -1057,6 +1058,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       resumeSessionId,
       envOverrides,
       effort,
+      historyLimit = DEFAULT_TMUX_HISTORY_LIMIT,
     } = options;
     const muxName = `codeman-${sessionId.slice(0, 8)}`;
 
@@ -1201,7 +1203,9 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
           }),
         // Raise tmux scrollback from its 2000-line default so re-attach preserves
         // more context. Matches the xterm-side default in constants.js.
-        execAsync(`${this.tmux()} set-option -t "${muxName}" history-limit 50000`, { timeout: EXEC_TIMEOUT_MS })
+        execAsync(`${this.tmux()} set-option -t "${muxName}" history-limit ${historyLimit}`, {
+          timeout: EXEC_TIMEOUT_MS,
+        })
           .then(() => {})
           .catch(() => {
             /* Non-critical — falls back to tmux default */
@@ -1324,6 +1328,7 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
       resumeSessionId,
       envOverrides,
       effort,
+      historyLimit = DEFAULT_TMUX_HISTORY_LIMIT,
     } = options;
     const session = this.sessions.get(sessionId);
     if (!session) return null;
@@ -1331,6 +1336,16 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
 
     if (!isValidMuxName(muxName) || !isValidPath(workingDir)) return null;
 
+    // Re-apply the configured tmux history-limit after respawn (kept in sync
+    // with the live setting via setHistoryLimit()).
+    if (!IS_TEST_MODE) {
+      await execAsync(`${this.tmux()} set-option -t ${shellescape(muxName)} history-limit ${historyLimit}`, {
+        timeout: EXEC_TIMEOUT_MS,
+      }).catch(() => {
+        /* Non-critical — keeps existing tmux history-limit */
+      });
+    }
+
     // Resolve CLI binary directory based on mode
     const { pathExport } = this.buildPathExport(mode);
 
@@ -1935,6 +1950,26 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
     }
   }
 
+  /**
+   * Apply a tmux history-limit to all tracked sessions (e.g. when the user
+   * changes the terminal-history setting). Invalid limits fall back to the
+   * default. Best-effort per session.
+   */
+  async setHistoryLimit(limit: number): Promise<void> {
+    const safeLimit = Number.isSafeInteger(limit) && limit > 0 ? Math.trunc(limit) : DEFAULT_TMUX_HISTORY_LIMIT;
+
+    if (IS_TEST_MODE) {
+      return;
+    }
+
+    const updates = Array.from(this.sessions.values()).map((session) =>
+      execAsync(`${this.tmux()} set-option -t ${shellescape(session.muxName)} history-limit ${safeLimit}`, {
+        timeout: EXEC_TIMEOUT_MS,
+      })
+    );
+    await Promise.allSettled(updates);
+  }
+
   /**
    * Send input directly to a tmux session using `send-keys`.
    *