feat(tools): salience-aware shell output compression — retain error lines through HeadTail (#67)

HeadTail now accepts an optional salience regex + cap: middle lines matching
it (error|fail|exception|panic|traceback|✗, case-insensitive) survive
truncation in place instead of being silently dropped, so a decisive error
buried in the middle of a long build/test log still reaches the model-facing
context entry. ShellTool's outputCompressor spec wires this in; the raw
build-gate receipt path is untouched.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

infrastructure/tools/src/main/kotlin/com/correx/infrastructure/tools/shell/ShellTool.kt

@@ -62,7 +62,11 @@ class ShellTool(
             // head/tail window holds distinct content rather than duplicates. Dedup is lossless
             // (count is preserved) and order-preserving, so it is safe as a default — unlike a
             // progress-dropping regex, which can silently eat real output.
-            listOf(StripBlankLines, CollapseConsecutiveDuplicates, HeadTail(HEAD_LINES, TAIL_LINES)),
+            listOf(
+                StripBlankLines,
+                CollapseConsecutiveDuplicates,
+                HeadTail(HEAD_LINES, TAIL_LINES, salience = SALIENCE_PATTERN),
+            ),
             bypassOnError = true,
         ),
     )
@@ -213,6 +217,9 @@ class ShellTool(
     private companion object {
         const val HEAD_LINES = 40
         const val TAIL_LINES = 40
+        // Case-insensitive: a decisive error line buried in the middle of a long build/test log
+        // (line 250 of 500) survives the head/tail window instead of being silently dropped.
+        const val SALIENCE_PATTERN = "error|fail|exception|panic|traceback|✗"
         const val EMPTY_MSG = "Missing or empty 'argv' parameter. Expected a JSON array of strings."
         val SHELL_BUILTINS = setOf("cd", "export", "source", ".", "pushd", "popd", "umask", "ulimit")
         val SHELL_OPERATORS = setOf("&&", "||", "|", ">", ">>", "<", ";", "&", "2>", "2>&1")