diff --git a/config.example.toml b/config.example.toml
index ffc1da282e..a0430c5cb9 100644
--- a/config.example.toml
+++ b/config.example.toml
@@ -769,9 +769,11 @@ exponential_base = 2.0
 # ─────────────────────────────────────────────────────────────────────────────────
 # Auto-compaction is a saved UI setting edited with `/config` (`auto_compact`).
 # The optional saved threshold setting is `auto_compact_threshold_percent`
-# (default 80). There is no config-file
-# `[compaction]` table yet; runtime compaction budgets are chosen by the TUI
-# from the active model/context window.
+# (default 80). `[compaction].enabled` is the engine-level replacement
+# compaction switch; when unset, the engine keeps using the saved auto_compact
+# behavior.
+[compaction]
+# enabled = true
 
 # Append-only Flash seams are experimental and opt-in while the v0.7.5
 # context/cache audit validates prefix-cache behavior.
@@ -785,6 +787,11 @@ l2_threshold = 384000
 l3_threshold = 576000
 seam_model = "deepseek-v4-flash"
 
+# Optional explicit alias for the context seam manager master switch. When set,
+# this overrides `[context].enabled`; thresholds and model stay under [context].
+# [seam_manager]
+# enabled = false
+
 # ─────────────────────────────────────────────────────────────────────────────────
 # Workshop / Large-Output Routing (#548)
 # ─────────────────────────────────────────────────────────────────────────────────
diff --git a/crates/tui/src/config.rs b/crates/tui/src/config.rs
index 94672fe8c3..7856d46aae 100644
--- a/crates/tui/src/config.rs
+++ b/crates/tui/src/config.rs
@@ -1682,6 +1682,22 @@ pub struct ContextConfig {
     pub seam_model: Option<String>,
 }
 
+/// Explicit Flash seam-manager switch.
+#[derive(Debug, Clone, Deserialize, Default)]
+pub struct SeamManagerConfig {
+    /// Overrides `[context].enabled` when set. Default: inherit context.enabled.
+    #[serde(default)]
+    pub enabled: Option<bool>,
+}
+
+/// Engine replacement-compaction switch.
+#[derive(Debug, Clone, Deserialize, Default)]
+pub struct CompactionRuntimeConfig {
+    /// Overrides the settings-derived auto-compaction default when set.
+    #[serde(default)]
+    pub enabled: Option<bool>,
+}
+
 /// Sub-agent model overrides. Keys in `models` can be role names (`worker`,
 /// `explorer`, `awaiter`) or type names (`general`, `explore`, `plan`,
 /// `review`, `custom`). Per-call explicit model choices still win.
@@ -1998,6 +2014,16 @@ pub struct Config {
     #[serde(default)]
     pub context: ContextConfig,
 
+    /// Explicit Flash seam-manager switch (#3765). This is a narrow alias for
+    /// `[context].enabled`; threshold/model fields stay under `[context]`.
+    #[serde(default, alias = "seamManager")]
+    pub seam_manager: SeamManagerConfig,
+
+    /// Engine replacement-compaction switch (#3765). When unset, the runtime
+    /// keeps using the settings-derived `auto_compact` behavior.
+    #[serde(default)]
+    pub compaction: CompactionRuntimeConfig,
+
     /// Agent Fleet trust/security/role/exec config.
     #[serde(default)]
     pub fleet: Option<codewhale_config::FleetConfigToml>,
@@ -3640,6 +3666,19 @@ impl Config {
         self.context.project_pack.unwrap_or(true)
     }
 
+    #[must_use]
+    pub fn seam_manager_enabled(&self) -> bool {
+        self.seam_manager
+            .enabled
+            .or(self.context.enabled)
+            .unwrap_or(false)
+    }
+
+    #[must_use]
+    pub fn compaction_enabled(&self, settings_default: bool) -> bool {
+        self.compaction.enabled.unwrap_or(settings_default)
+    }
+
     /// Return whether shell execution is allowed. Defaults to `false`: shell
     /// access must be opted into explicitly (GHSA-72w5-pf8h-xfp4).
     #[must_use]
@@ -5536,6 +5575,15 @@ fn merge_config(base: Config, override_cfg: Config) -> Config {
                 .or(base.context.l3_threshold),
             seam_model: override_cfg.context.seam_model.or(base.context.seam_model),
         },
+        seam_manager: SeamManagerConfig {
+            enabled: override_cfg
+                .seam_manager
+                .enabled
+                .or(base.seam_manager.enabled),
+        },
+        compaction: CompactionRuntimeConfig {
+            enabled: override_cfg.compaction.enabled.or(base.compaction.enabled),
+        },
         fleet: override_cfg.fleet.or(base.fleet),
         subagents: override_cfg.subagents.or(base.subagents),
         strict_tool_mode: override_cfg.strict_tool_mode.or(base.strict_tool_mode),
diff --git a/crates/tui/src/config/tests.rs b/crates/tui/src/config/tests.rs
index 1ca12a4f12..4064648a05 100644
--- a/crates/tui/src/config/tests.rs
+++ b/crates/tui/src/config/tests.rs
@@ -3509,6 +3509,7 @@ fn normalize_model_name_accepts_provider_prefixed_deepseek_ids() {
 fn default_context_seams_are_opt_in() {
     let config = Config::default();
     assert!(!config.context.enabled.unwrap_or(false));
+    assert!(!config.seam_manager_enabled());
     assert_eq!(config.context.l1_threshold.unwrap_or(192_000), 192_000);
     assert_eq!(
         config
@@ -3520,6 +3521,57 @@ fn default_context_seams_are_opt_in() {
     );
 }
 
+#[test]
+fn seam_manager_enabled_can_use_dedicated_table() -> Result<()> {
+    let config: Config = toml::from_str(
+        r#"
+        [context]
+        enabled = true
+
+        [seam_manager]
+        enabled = false
+        "#,
+    )?;
+
+    assert_eq!(config.context.enabled, Some(true));
+    assert_eq!(config.seam_manager.enabled, Some(false));
+    assert!(!config.seam_manager_enabled());
+
+    let config: Config = toml::from_str(
+        r#"
+        [seam_manager]
+        enabled = true
+        "#,
+    )?;
+
+    assert!(config.seam_manager_enabled());
+    Ok(())
+}
+
+#[test]
+fn compaction_enabled_uses_config_override_when_present() -> Result<()> {
+    let config = Config::default();
+    assert!(config.compaction_enabled(true));
+    assert!(!config.compaction_enabled(false));
+
+    let disabled: Config = toml::from_str(
+        r#"
+        [compaction]
+        enabled = false
+        "#,
+    )?;
+    assert!(!disabled.compaction_enabled(true));
+
+    let enabled: Config = toml::from_str(
+        r#"
+        [compaction]
+        enabled = true
+        "#,
+    )?;
+    assert!(enabled.compaction_enabled(false));
+    Ok(())
+}
+
 #[test]
 fn profile_without_context_does_not_disable_base_context() {
     let mut profiles = HashMap::new();
@@ -3539,6 +3591,28 @@ fn profile_without_context_does_not_disable_base_context() {
     assert_eq!(merged.context.enabled, Some(true));
 }
 
+#[test]
+fn profile_without_context_gates_does_not_disable_base_gates() {
+    let mut profiles = HashMap::new();
+    profiles.insert("work".to_string(), Config::default());
+    let config = ConfigFile {
+        base: Config {
+            seam_manager: SeamManagerConfig {
+                enabled: Some(true),
+            },
+            compaction: CompactionRuntimeConfig {
+                enabled: Some(false),
+            },
+            ..Default::default()
+        },
+        profiles: Some(profiles),
+    };
+
+    let merged = apply_profile(config, Some("work")).expect("profile");
+    assert_eq!(merged.seam_manager.enabled, Some(true));
+    assert_eq!(merged.compaction.enabled, Some(false));
+}
+
 #[test]
 fn profile_skills_config_merges_individual_fields() {
     let mut profiles = HashMap::new();
diff --git a/crates/tui/src/config_ui.rs b/crates/tui/src/config_ui.rs
index 7e4e7bbb5f..2f5bf572bd 100644
--- a/crates/tui/src/config_ui.rs
+++ b/crates/tui/src/config_ui.rs
@@ -658,6 +658,7 @@ fn validate_document(doc: &ConfigUiDocument) -> Result<()> {
 fn reload_runtime_config(app: &mut App, config: &mut Config) -> Result<()> {
     let reloaded = Config::load(app.config_path.clone(), app.config_profile.as_deref())?;
     *config = reloaded.clone();
+    app.refresh_config_runtime_overrides(config);
     app.api_provider = reloaded.api_provider();
     app.reasoning_effort =
         ReasoningEffort::from_setting(reloaded.reasoning_effort().unwrap_or_else(|| {
diff --git a/crates/tui/src/core/engine.rs b/crates/tui/src/core/engine.rs
index db0765d3bd..6db674efb7 100644
--- a/crates/tui/src/core/engine.rs
+++ b/crates/tui/src/core/engine.rs
@@ -916,7 +916,7 @@ impl Engine {
         // is worth the extra request and transcript mutation.
         let seam_manager = deepseek_client.as_ref().map(|main_client| {
             let seam_config = SeamConfig {
-                enabled: api_config.context.enabled.unwrap_or(false),
+                enabled: api_config.seam_manager_enabled(),
                 verbatim_window_turns: api_config
                     .context
                     .verbatim_window_turns
diff --git a/crates/tui/src/main.rs b/crates/tui/src/main.rs
index eb0e70f8fb..00a995bc62 100644
--- a/crates/tui/src/main.rs
+++ b/crates/tui/src/main.rs
@@ -7027,7 +7027,7 @@ async fn run_exec_agent(
         )
     };
     let compaction = CompactionConfig {
-        enabled: auto_compact_enabled,
+        enabled: execution_config.compaction_enabled(auto_compact_enabled),
         model: effective_model.clone(),
         token_threshold: crate::route_budget::compaction_threshold_for_route_at_percent(
             effective_provider,
diff --git a/crates/tui/src/runtime_threads.rs b/crates/tui/src/runtime_threads.rs
index 632de12e9b..d795d8c48d 100644
--- a/crates/tui/src/runtime_threads.rs
+++ b/crates/tui/src/runtime_threads.rs
@@ -874,7 +874,7 @@ impl RuntimeThreadManager {
                     )
                 };
             let compaction = crate::compaction::CompactionConfig {
-                enabled: auto_compact_enabled,
+                enabled: cfg.compaction_enabled(auto_compact_enabled),
                 model: String::new(), // per-engine, filled below
                 token_threshold: compaction_threshold_for_model_at_percent(
                     &cfg.default_text_model.clone().unwrap_or_default(),
@@ -2506,7 +2506,7 @@ impl RuntimeThreadManager {
                 auto_compact_default_for_model(&thread.model)
             };
         let compaction = CompactionConfig {
-            enabled: auto_compact_enabled,
+            enabled: cfg.compaction_enabled(auto_compact_enabled),
             model: thread.model.clone(),
             token_threshold: compaction_threshold_for_model_at_percent(
                 &thread.model,
diff --git a/crates/tui/src/tui/app.rs b/crates/tui/src/tui/app.rs
index 9157275964..9e18bae425 100644
--- a/crates/tui/src/tui/app.rs
+++ b/crates/tui/src/tui/app.rs
@@ -1696,6 +1696,7 @@ pub struct App {
     #[allow(dead_code)]
     pub system_prompt: Option<SystemPrompt>,
     pub auto_compact: bool,
+    pub compaction_enabled_override: Option<bool>,
     pub auto_compact_user_configured: bool,
     pub auto_compact_threshold_percent: f64,
     pub calm_mode: bool,
@@ -2628,6 +2629,7 @@ impl App {
             bracketed_paste_seen: false,
             system_prompt: None,
             auto_compact,
+            compaction_enabled_override: config.compaction.enabled,
             auto_compact_user_configured,
             auto_compact_threshold_percent,
             calm_mode,
@@ -5692,13 +5694,22 @@ impl App {
 
     pub fn compaction_config(&self) -> CompactionConfig {
         CompactionConfig {
-            enabled: self.auto_compact,
+            enabled: self.automatic_compaction_enabled(),
             token_threshold: self.compact_threshold,
             model: self.effective_model_for_budget().to_string(),
             ..Default::default()
         }
     }
 
+    pub fn automatic_compaction_enabled(&self) -> bool {
+        self.compaction_enabled_override
+            .unwrap_or(self.auto_compact)
+    }
+
+    pub fn refresh_config_runtime_overrides(&mut self, config: &Config) {
+        self.compaction_enabled_override = config.compaction.enabled;
+    }
+
     pub fn fallback_chain_entries(&self) -> Vec<(usize, ApiProvider, bool)> {
         let Some(chain) = &self.provider_chain else {
             return Vec::new();
diff --git a/crates/tui/src/tui/app/tests.rs b/crates/tui/src/tui/app/tests.rs
index 57198747f6..e2d913665b 100644
--- a/crates/tui/src/tui/app/tests.rs
+++ b/crates/tui/src/tui/app/tests.rs
@@ -1,5 +1,7 @@
 use super::*;
-use crate::config::{ApiProvider, Config, ProviderConfig, ProvidersConfig};
+use crate::config::{
+    ApiProvider, CompactionRuntimeConfig, Config, ProviderConfig, ProvidersConfig,
+};
 use crate::test_support::{EnvVarGuard, lock_test_env};
 use crate::tools::plan::{PlanItemArg, StepStatus, UpdatePlanArgs};
 use crate::tools::todo::TodoStatus;
@@ -1955,6 +1957,51 @@ fn test_compaction_config() {
     assert_eq!(config.model, "deepseek-v4-flash");
 }
 
+#[test]
+fn compaction_config_respects_config_enabled_override() {
+    let config = Config {
+        compaction: CompactionRuntimeConfig {
+            enabled: Some(false),
+        },
+        ..Default::default()
+    };
+    let mut app = App::new(test_options(false), &config);
+    app.auto_compact = true;
+    assert!(!app.compaction_config().enabled);
+
+    let config = Config {
+        compaction: CompactionRuntimeConfig {
+            enabled: Some(true),
+        },
+        ..Default::default()
+    };
+    let mut app = App::new(test_options(false), &config);
+    app.auto_compact = false;
+    assert!(app.compaction_config().enabled);
+}
+
+#[test]
+fn app_refreshes_compaction_override_from_runtime_config() {
+    let mut app = App::new(test_options(false), &Config::default());
+    app.compaction_enabled_override = Some(true);
+
+    let config = Config {
+        compaction: CompactionRuntimeConfig {
+            enabled: Some(false),
+        },
+        ..Default::default()
+    };
+    app.refresh_config_runtime_overrides(&config);
+    assert_eq!(app.compaction_enabled_override, Some(false));
+    assert!(!app.automatic_compaction_enabled());
+
+    let config = Config::default();
+    app.auto_compact = true;
+    app.refresh_config_runtime_overrides(&config);
+    assert_eq!(app.compaction_enabled_override, None);
+    assert!(app.automatic_compaction_enabled());
+}
+
 #[test]
 fn test_update_model_compaction_budget() {
     let mut app = App::new(test_options(false), &Config::default());
diff --git a/crates/tui/src/tui/ui.rs b/crates/tui/src/tui/ui.rs
index a71aec4699..234308ad66 100644
--- a/crates/tui/src/tui/ui.rs
+++ b/crates/tui/src/tui/ui.rs
@@ -7654,6 +7654,7 @@ async fn apply_command_result(
                 match Config::load(app.config_path.clone(), Some(&profile)) {
                     Ok(new_config) => {
                         *config = new_config.clone();
+                        app.refresh_config_runtime_overrides(config);
                         app.api_provider = config.api_provider();
                         let new_model = config.default_model();
                         app.set_model_selection(new_model.clone());
@@ -10636,8 +10637,8 @@ fn maybe_warn_context_pressure(app: &mut App) {
         return;
     }
 
-    let recommendation = if !app.auto_compact {
-        "Consider enabling auto_compact or use /compact."
+    let recommendation = if !app.automatic_compaction_enabled() {
+        "Automatic compaction is disabled; use /compact or enable auto_compact/[compaction].enabled."
     } else if percent >= configured_threshold {
         "Auto-compaction will run before the next send."
     } else {
@@ -10664,7 +10665,7 @@ fn maybe_warn_context_pressure(app: &mut App) {
 }
 
 fn should_auto_compact_before_send(app: &App) -> bool {
-    if !app.auto_compact {
+    if !app.automatic_compaction_enabled() {
         return false;
     }
     context_usage_snapshot(app)
diff --git a/crates/tui/src/tui/ui/tests.rs b/crates/tui/src/tui/ui/tests.rs
index bc570dfc62..84c92ad0d9 100644
--- a/crates/tui/src/tui/ui/tests.rs
+++ b/crates/tui/src/tui/ui/tests.rs
@@ -5732,6 +5732,18 @@ fn should_auto_compact_before_send_respects_threshold_and_setting() {
     app.auto_compact = false;
     assert!(!should_auto_compact_before_send(&app));
 
+    // The config.toml engine switch is a hard gate for automatic pre-send
+    // compaction, independent of the saved UI auto_compact setting.
+    app.auto_compact = true;
+    app.auto_compact_threshold_percent = 70.0;
+    app.compaction_enabled_override = Some(false);
+    assert!(!should_auto_compact_before_send(&app));
+
+    app.auto_compact = false;
+    app.compaction_enabled_override = Some(true);
+    assert!(should_auto_compact_before_send(&app));
+    app.compaction_enabled_override = None;
+
     // Small estimated context + auto_compact ON can trigger once the
     // configured percent threshold is crossed. This still matches the
     // #115 fix: the estimate is the primary signal, not the engine's
@@ -5770,6 +5782,26 @@ fn context_pressure_warning_reflects_auto_compact_threshold_state() {
         status.contains("Auto-compaction will run before the next send."),
         "unexpected status: {status}"
     );
+
+    let mut app = create_test_app();
+    app.api_messages = vec![Message {
+        role: "user".to_string(),
+        content: vec![ContentBlock::Text {
+            text: "context ".repeat(240_000),
+            cache_control: None,
+        }],
+    }];
+    app.auto_compact = true;
+    app.compaction_enabled_override = Some(false);
+    app.auto_compact_threshold_percent = 70.0;
+
+    maybe_warn_context_pressure(&mut app);
+
+    let status = app.status_message.expect("context warning");
+    assert!(
+        status.contains("Automatic compaction is disabled"),
+        "unexpected status: {status}"
+    );
 }
 
 // ============================================================================
diff --git a/docs/CONFIGURATION.md b/docs/CONFIGURATION.md
index efddaa9189..865346a0d0 100644
--- a/docs/CONFIGURATION.md
+++ b/docs/CONFIGURATION.md
@@ -933,7 +933,9 @@ policy for known context windows up to the 1M-token V4 class. Automatic
 compaction runs before the active model limit and carries the compacted summary
 forward into the next request. The trigger defaults to
 `auto_compact_threshold_percent = 80`. Users who prefer manual continuity can
-persist `auto_compact = false`; manual `/compact` / Ctrl+L remains available.
+persist `auto_compact = false`; `[compaction].enabled = false` is the
+engine-level config.toml switch for replacement compaction. Manual `/compact` /
+Ctrl+L remains available.
 You can inspect or update these from the TUI with `/settings` and `/config`
 (interactive editor).
 
@@ -1021,12 +1023,13 @@ separate:
 | Cost estimate | Approximate spend from provider usage and configured DeepSeek rates. | Display only. |
 
 For known context-window models, including 1M-class V4 models, replacement
-compaction is enabled by default unless the user explicitly configures
-`auto_compact = false`. It fires at the active model's compaction threshold and
-replays the generated summary through the stable system prompt on the next
-request. Unknown model ids remain opt-in. The Flash seam manager remains opt-in
-(`[context].enabled = false`), and the capacity controller remains disabled
-unless configured.
+compaction follows `[compaction].enabled` when explicitly configured; otherwise
+it keeps the existing `auto_compact` settings behavior. It fires at the active
+model's compaction threshold and replays the generated summary through the
+stable system prompt on the next request. Unknown model ids remain opt-in. The
+Flash seam manager remains disabled by default; `[context].enabled` opts in,
+and `[seam_manager].enabled` can explicitly override that master switch. The
+capacity controller remains disabled unless configured.
 
 ### Command Migration Notes
 
@@ -1266,6 +1269,10 @@ If you are upgrading from older releases:
     `~/.codewhale/snapshots/<project_hash>/<worktree_hash>/.git`, with legacy
     `~/.deepseek/snapshots/...` fallback when only the legacy state exists, and
     never use the workspace's own `.git` directory
+- `compaction.*` (optional): replacement compaction engine switch:
+  - `[compaction].enabled` (bool, default unset): when set, overrides the
+    settings-derived `auto_compact` engine switch. Set `false` for full manual
+    control over automatic replacement compaction.
 - `context.*` (optional): append-only Fin seam manager, currently opt-in.
   Fin is the fast `deepseek-v4-flash` path with thinking off used for
   coordination work such as routing, summaries, and context maintenance.
@@ -1277,6 +1284,11 @@ If you are upgrading from older releases:
   - `[context].l2_threshold` (int, default `384000`)
   - `[context].l3_threshold` (int, default `576000`)
   - `[context].seam_model` (string, default `deepseek-v4-flash`)
+- `seam_manager.*` (optional): explicit alias for the Flash seam manager master
+  switch:
+  - `[seam_manager].enabled` (bool, default unset): overrides
+    `[context].enabled` when set. Thresholds and model remain under
+    `[context]`.
 - `retry.*` (optional): retry/backoff settings for API requests:
   - `[retry].enabled` (bool, default `true`)
   - `[retry].max_retries` (int, default `3`)