refactor(tui): extract checkpoint recognition to leaf module

crates/tui/src/compaction.rs

@@ -160,17 +160,18 @@ by that language model. Use this to build on the work that has already been done
 duplicating work. Here is the summary produced by the other language model, use the information \
 in this summary to assist with your own analysis:";
 
-/// Detection marker for committed compaction-summary text: the stable first
-/// sentence of `SUMMARY_HEADER`. `engine/context.rs` restores summaries by
-/// the same marker on session load.
-pub const COMPACTION_SUMMARY_MARKER: &str = "Another language model started to solve this problem";
-/// Marker written by pre-v0.9.6 compaction; sessions saved under the old
-/// format must still be recognized so their summary is replaced, not stacked.
-pub const LEGACY_COMPACTION_SUMMARY_MARKER: &str = "Conversation Summary (Auto-Generated)";
-const COMPACTION_CHECKPOINT_PROVENANCE: &str = "<!-- codewhale.compaction-checkpoint.v1 -->";
 const COMPACTION_SUMMARY_BEGIN: &str = "<!-- compaction-summary:begin -->";
 const COMPACTION_SUMMARY_END: &str = "<!-- compaction-summary:end -->";
 
+// The checkpoint-recognition family lives in the `history_recognition` leaf so
+// `compaction` and `runtime_handoff` can share it without a module cycle; the
+// names below stay reachable on the `compaction` path.
+pub(crate) use crate::history_recognition::{
+    COMPACTION_CHECKPOINT_PROVENANCE, is_compaction_checkpoint_message,
+    is_generated_compaction_checkpoint,
+};
+pub use crate::history_recognition::{COMPACTION_SUMMARY_MARKER, LEGACY_COMPACTION_SUMMARY_MARKER};
+
 /// Whether a system-prompt text block is a committed compaction summary.
 #[must_use]
 pub fn is_compaction_summary_text(text: &str) -> bool {
@@ -296,77 +297,6 @@ pub(crate) fn compaction_checkpoint_message(prompt: &SystemPrompt) -> Message {
     }
 }
 
-/// Whether the first text block carries the summary header, current or legacy.
-fn has_compaction_summary_header(text: &str) -> bool {
-    // `COMPACTION_SUMMARY_MARKER` is the current header's first sentence, and
-    // releases before this one also committed carriers with their own body
-    // after that sentence, so the prefix — not the whole header — is the
-    // stable shape.
-    text.starts_with(COMPACTION_SUMMARY_MARKER)
-        || text.starts_with(LEGACY_COMPACTION_SUMMARY_MARKER)
-}
-
-/// Structural recognition of the one generated checkpoint in saved history.
-///
-/// The marker substring scan above stays scoped to system-prompt carriers:
-/// on history it matches an ordinary user turn that merely *quotes* the
-/// header, and every consumer here either deletes or replaces what it matches.
-/// Structure instead — a `role="user"` message whose first text block begins
-/// with the header and whose remaining block, if any, is exactly the
-/// engine-written provenance marker.
-///
-/// Boundary: the single-block form has no provenance to check, because
-/// releases before this one saved the bare summary, and a reload that failed
-/// to recognize it would stack a second summary beside it. A user turn that
-/// *begins* with the header is therefore still read as a carrier here. Request
-/// rewriting does not share that reading — see
-/// [`is_generated_compaction_checkpoint`] — so such a turn is never moved or
-/// merged on the wire.
-#[must_use]
-pub(crate) fn is_compaction_checkpoint_message(message: &Message) -> bool {
-    let [
-        ContentBlock::Text {
-            text,
-            cache_control: None,
-        },
-        rest @ ..,
-    ] = message.content.as_slice()
-    else {
-        return false;
-    };
-    message.role == Role::User
-        && has_compaction_summary_header(text)
-        && (rest.is_empty()
-            || matches!(
-                rest,
-                [ContentBlock::Text {
-                    text: provenance,
-                    cache_control: None,
-                }] if provenance == COMPACTION_CHECKPOINT_PROVENANCE
-            ))
-}
-
-/// The provenance-stamped form, and the only form request rewriting may
-/// relocate or merge. A user cannot type this shape, so an ordinary turn that
-/// pastes the whole summary header after a tool result keeps its position.
-#[must_use]
-pub(crate) fn is_generated_compaction_checkpoint(message: &Message) -> bool {
-    let [
-        ContentBlock::Text {
-            cache_control: None,
-            ..
-        },
-        ContentBlock::Text {
-            text: provenance,
-            cache_control: None,
-        },
-    ] = message.content.as_slice()
-    else {
-        return false;
-    };
-    provenance == COMPACTION_CHECKPOINT_PROVENANCE && is_compaction_checkpoint_message(message)
-}
-
 /// Replace the saved history checkpoint with the authoritative carrier, keep
 /// its position relative to later turns, and repair a pre-placement-fix
 /// Agent-topology sidecar. Both steps exist so the first request after a

crates/tui/src/history_recognition.rs

@@ -0,0 +1,94 @@
+//! Structural recognition of the compaction checkpoint in saved history.
+//!
+//! Leaf module shared by `compaction` and `runtime_handoff`. Hosting the
+//! checkpoint-recognition family here keeps `runtime_handoff`'s production
+//! code from importing `compaction` (its tests still build carriers through
+//! `compaction`'s constructors): `compaction` already imports
+//! `runtime_handoff` for restore-time topology relocation, so a reverse edge
+//! would close a module dependency cycle.
+
+use crate::models::{ContentBlock, Message, Role};
+
+/// Detection marker for committed compaction-summary text: the stable first
+/// sentence of the summary header `compaction` commits (`SUMMARY_HEADER`).
+/// `engine/context.rs` restores summaries by the same marker on session load.
+pub const COMPACTION_SUMMARY_MARKER: &str = "Another language model started to solve this problem";
+/// Marker written by pre-v0.9.6 compaction; sessions saved under the old
+/// format must still be recognized so their summary is replaced, not stacked.
+pub const LEGACY_COMPACTION_SUMMARY_MARKER: &str = "Conversation Summary (Auto-Generated)";
+pub(crate) const COMPACTION_CHECKPOINT_PROVENANCE: &str =
+    "<!-- codewhale.compaction-checkpoint.v1 -->";
+
+/// Whether the first text block carries the summary header, current or legacy.
+fn has_compaction_summary_header(text: &str) -> bool {
+    // `COMPACTION_SUMMARY_MARKER` is the current header's first sentence, and
+    // releases before this one also committed carriers with their own body
+    // after that sentence, so the prefix — not the whole header — is the
+    // stable shape.
+    text.starts_with(COMPACTION_SUMMARY_MARKER)
+        || text.starts_with(LEGACY_COMPACTION_SUMMARY_MARKER)
+}
+
+/// Structural recognition of the one generated checkpoint in saved history.
+///
+/// The marker substring scan in `compaction` (`is_compaction_summary_text`)
+/// stays scoped to system-prompt carriers:
+/// on history it matches an ordinary user turn that merely *quotes* the
+/// header, and the consumers that match on history — `compaction` restore,
+/// `runtime_handoff` placement and edit-guarding — replace what they match
+/// or must protect it from deletion.
+/// Structure instead — a `role="user"` message whose first text block begins
+/// with the header and whose remaining block, if any, is exactly the
+/// engine-written provenance marker.
+///
+/// Boundary: the single-block form has no provenance to check, because
+/// releases before this one saved the bare summary, and a reload that failed
+/// to recognize it would stack a second summary beside it. A user turn that
+/// *begins* with the header is therefore still read as a carrier here. Request
+/// rewriting does not share that reading — see
+/// [`is_generated_compaction_checkpoint`] — so such a turn is never moved or
+/// merged on the wire.
+#[must_use]
+pub(crate) fn is_compaction_checkpoint_message(message: &Message) -> bool {
+    let [
+        ContentBlock::Text {
+            text,
+            cache_control: None,
+        },
+        rest @ ..,
+    ] = message.content.as_slice()
+    else {
+        return false;
+    };
+    message.role == Role::User
+        && has_compaction_summary_header(text)
+        && (rest.is_empty()
+            || matches!(
+                rest,
+                [ContentBlock::Text {
+                    text: provenance,
+                    cache_control: None,
+                }] if provenance == COMPACTION_CHECKPOINT_PROVENANCE
+            ))
+}
+
+/// The provenance-stamped form, and the only form request rewriting may
+/// relocate or merge. A user cannot type this shape, so an ordinary turn that
+/// pastes the whole summary header after a tool result keeps its position.
+#[must_use]
+pub(crate) fn is_generated_compaction_checkpoint(message: &Message) -> bool {
+    let [
+        ContentBlock::Text {
+            cache_control: None,
+            ..
+        },
+        ContentBlock::Text {
+            text: provenance,
+            cache_control: None,
+        },
+    ] = message.content.as_slice()
+    else {
+        return false;
+    };
+    provenance == COMPACTION_CHECKPOINT_PROVENANCE && is_compaction_checkpoint_message(message)
+}

crates/tui/src/lib.rs

@@ -70,6 +70,7 @@ pub use fleet::profile::WORKSPACE_AGENT_PROFILE_DIR;
 pub use fleet::roster::FleetRoster;
 mod goal_loop;
 mod hashing;
+mod history_recognition;
 #[doc(hidden)]
 pub mod hooks;
 mod image_attach;

crates/tui/src/runtime_handoff.rs

@@ -805,7 +805,7 @@ pub(crate) fn replace_agent_topology_checkpoint(
     let ends_with_tool_result = messages.last().is_some_and(carries_tool_result);
     let ends_with_compaction_summary = messages
         .last()
-        .is_some_and(crate::compaction::is_generated_compaction_checkpoint);
+        .is_some_and(crate::history_recognition::is_generated_compaction_checkpoint);
     let position = if ends_with_tool_result || ends_with_compaction_summary {
         compaction_anchor(messages, messages.len()).map_or(0, CompactionAnchor::placement_index)
     } else {
@@ -1328,7 +1328,7 @@ fn is_compaction_topology_carrier(message: &Message) -> bool {
 fn restored_topology_anchor(messages: &[Message], index: usize) -> Option<usize> {
     let summary_before = messages[..index]
         .iter()
-        .rposition(crate::compaction::is_compaction_checkpoint_message);
+        .rposition(crate::history_recognition::is_compaction_checkpoint_message);
     let follows_tool_result = index > 0 && carries_tool_result(&messages[index - 1]);
     if summary_before.is_none() && !follows_tool_result {
         return None;
@@ -1337,7 +1337,7 @@ fn restored_topology_anchor(messages: &[Message], index: usize) -> Option<usize>
         .or_else(|| {
             messages[index + 1..]
                 .iter()
-                .position(crate::compaction::is_compaction_checkpoint_message)
+                .position(crate::history_recognition::is_compaction_checkpoint_message)
                 .map(|offset| index + 1 + offset)
         })
         .unwrap_or(messages.len());
@@ -1480,7 +1480,7 @@ fn is_runtime_owned_user_message(message: &Message) -> bool {
         // The compaction checkpoint is engine-written history, so `/edit` must
         // not treat it as the turn to truncate at: doing so deletes the summary
         // the session is built on. Structure decides, not the marker substring.
-        || crate::compaction::is_compaction_checkpoint_message(message)
+        || crate::history_recognition::is_compaction_checkpoint_message(message)
 }
 
 /// Return engine-owned metadata in either the current trailing shape or the