fix(compaction): keep last tool round and unstick CI (#4394)

Drop the unused validate_last_round_coverage re-export that failed Lint.
Walk last_round_start back to the last tool-bearing user round instead of
one hop, so two trailing toolless turns cannot drop a tool result behind
the summary. Sync the TUI changelog slice with root.

Add a language-invariant fixture matrix and a Node coverage validator
next to the survival contract. There is no Go runtime in this repository
yet.

Evidence:
  cargo check -p codewhale-tui --locked
  cargo clippy -p codewhale-tui --lib --locked -- -A clippy::all -D unused-imports
  cargo test -p codewhale-tui --lib --offline --locked -- compaction context_inspector last_round
    -> 128 passed; 0 failed
  node crates/tui/src/compaction/validate_survival_contract.mjs
    -> ok 9 survival-contract fixtures

Refs: #4394
Signed-off-by: CodeWhale Bot <bot@codewhale.net>

Author: CodeWhale Bot

crates/tui/CHANGELOG.md

@@ -14,7 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Compaction replacement history keeps a bounded last user round (assistant +
   tool results) instead of dropping them behind a summary. `/context` names
-  the compaction path and `/anchor` survival (#4394).
+  the compaction path and `/anchor` survival. Failed compact still does not
+  replace live history (#4394).
 
 - TUI: startup no longer presents an approximate ASCII or block-glyph whale as
   the product mark. It keeps the direct Tideline prompt while exact-raster
@@ -27,8 +28,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Compaction publishes a structured survival contract for session-tree
-  journal entry types (`src/compaction/SURVIVAL_CONTRACT.md`) and fails
-  closed when the last user round, tool results, `/anchor` text, or
+  journal entry types (`crates/tui/src/compaction/SURVIVAL_CONTRACT.md`) and
+  fails closed when the last user round, tool results, `/anchor` text, or
   checkpoint receipt would vanish (#4394).
 
 - Website: the public site moves to the Tideline deep-ocean design language

crates/tui/src/compaction.rs

@@ -18,11 +18,11 @@ mod last_round;
 #[cfg(test)]
 #[path = "compaction/survival_contract.rs"]
 mod survival_contract;
+pub(crate) use last_round::last_round_start;
 pub use last_round::{
     CompactionCoverage, CompactionKeep, CompactionPath, LastCompactionSnapshot,
     inspect_compaction_keep, last_round_kept_count, pinned_anchors_text,
 };
-pub(crate) use last_round::{last_round_start, validate_last_round_coverage};
 
 /// Configuration for conversation compaction behavior.
 ///
@@ -2037,7 +2037,8 @@ mod tests {
             user_text_of(retained.last().unwrap()).as_deref(),
             Some(text.as_str())
         );
-        validate_last_round_coverage(&messages, &retained[..retained.len() - 1]).unwrap();
+        last_round::validate_last_round_coverage(&messages, &retained[..retained.len() - 1])
+            .unwrap();
     }
 
     #[test]
@@ -2047,7 +2048,7 @@ mod tests {
             msg("assistant", "session_store::roundtrip panics on reload."),
         ];
         let gutting = vec![msg("user", "What failed?")];
-        let error = validate_last_round_coverage(&original, &gutting)
+        let error = last_round::validate_last_round_coverage(&original, &gutting)
             .expect_err("dropping last-round assistant text must fail closed");
         assert!(error.to_string().contains("assistant"), "{error}");
     }

crates/tui/src/compaction/SURVIVAL_CONTRACT.md

@@ -67,7 +67,9 @@ work.
 Rust now:
 
 - `last_round::build_replacement_history` keeps the bounded last user round
-  (assistant + tool results) and appends one checkpoint receipt.
+  (assistant + tool results) and appends one checkpoint receipt. A trailing
+  toolless user/assistant tail still walks back to the last tool-bearing
+  round; chat-only sessions keep only the latest user turn.
 - `validate_last_round_coverage` refuses the rewrite if that round's user
   text, tool-result ids, or assistant output would vanish.
 - `validate_survival_contract` also refuses a missing checkpoint receipt,
@@ -76,4 +78,11 @@ Rust now:
 - `compact_messages_safe` never mutates the caller's live history; the host
   commits only after `Ok`.
 
+The language-invariant fixture matrix is
+`crates/tui/src/compaction/fixtures/matrix.json`. Rust loads it in
+`last_round` tests. `validate_survival_contract.mjs` is the same coverage
+floor for a later TypeScript strategy (`node validate_survival_contract.mjs`).
+There is no Go runtime in this repository yet; a Go validator remains a
+follow-up when a Go strategy exists.
+
 `/context` names the compaction path and `/anchor` survival.

crates/tui/src/compaction/fixtures/matrix.json

@@ -0,0 +1,163 @@
+{
+  "schema_version": 1,
+  "cases": [
+    {
+      "id": "last-round-tools-kept",
+      "expect": "pass",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Running."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "test session_store::roundtrip ... FAILED"}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Running."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "test session_store::roundtrip ... FAILED"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: suite still failing"}]}
+      ]
+    },
+    {
+      "id": "last-round-tools-dropped",
+      "expect": "fail",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Running."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "test session_store::roundtrip ... FAILED"}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: and kept going"}]}
+      ]
+    },
+    {
+      "id": "last-round-assistant-dropped",
+      "expect": "fail",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "What failed?"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "session_store::roundtrip panics on reload."}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "What failed?"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: missing assistant"}]}
+      ]
+    },
+    {
+      "id": "toolless-tail-keeps-prior-tools",
+      "expect": "pass",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Running."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "test session_store::roundtrip ... FAILED"}]},
+        {"role": "user", "content": [{"type": "text", "text": "ok thanks"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "you're welcome"}]},
+        {"role": "user", "content": [{"type": "text", "text": "one more thing"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "sure"}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Running."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "test session_store::roundtrip ... FAILED"}]},
+        {"role": "user", "content": [{"type": "text", "text": "ok thanks"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "you're welcome"}]},
+        {"role": "user", "content": [{"type": "text", "text": "one more thing"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "sure"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: keep the failing test result"}]}
+      ]
+    },
+    {
+      "id": "toolless-tail-drops-prior-tools",
+      "expect": "fail",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the failing test."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Running."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "test session_store::roundtrip ... FAILED"}]},
+        {"role": "user", "content": [{"type": "text", "text": "ok thanks"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "you're welcome"}]},
+        {"role": "user", "content": [{"type": "text", "text": "one more thing"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "sure"}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "one more thing"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "sure"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: dropped the tool round"}]}
+      ]
+    },
+    {
+      "id": "chat-only-last-round",
+      "expect": "pass",
+      "last_round_start": 2,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "hello"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "hi"}]},
+        {"role": "user", "content": [{"type": "text", "text": "how are you"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "fine"}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "how are you"}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "fine"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: continued the chat"}]}
+      ]
+    },
+    {
+      "id": "dropped-anchor",
+      "expect": "fail",
+      "anchors": "ship 0.9.12",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "Keep the pin."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Anchored."}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "Keep the pin."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Anchored."}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: progress without the pin"}]}
+      ]
+    },
+    {
+      "id": "missing-receipt",
+      "expect": "fail",
+      "anchors": "ship 0.9.12",
+      "last_round_start": 0,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "Keep the pin."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Anchored."}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "Keep the pin."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Anchored."}]}
+      ]
+    },
+    {
+      "id": "duplicate-checkpoint",
+      "expect": "fail",
+      "last_round_start": 1,
+      "original": [
+        {"role": "user", "content": [{"type": "text", "text": "older"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Run the suite now."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Rerunning."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "ok"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: first handoff"}]}
+      ],
+      "replacement": [
+        {"role": "user", "content": [{"type": "text", "text": "Run the suite now."}]},
+        {"role": "assistant", "content": [{"type": "text", "text": "Rerunning."}]},
+        {"role": "assistant", "content": [{"type": "tool_use", "id": "live", "name": "Bash", "input": {"command": "cargo test"}}]},
+        {"role": "user", "content": [{"type": "tool_result", "tool_use_id": "live", "content": "ok"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: first handoff"}]},
+        {"role": "user", "content": [{"type": "text", "text": "Another language model started to solve this problem: second handoff"}]}
+      ]
+    }
+  ]
+}