feat(tools): collapse-consecutive-duplicates compression rule

adr-0003 §1.3 dedup: collapse runs of identical adjacent lines into `line (×N)`, order-preserving and lossless (count retained). Wired into ShellTool's default spec before HeadTail so the head/tail window holds distinct content. Safe as a default, unlike DropMatching.

core/tools/src/main/kotlin/com/correx/core/tools/compression/DeclarativeCompressor.kt

@@ -1,5 +1,6 @@
 package com.correx.core.tools.compression
 
+import com.correx.core.tools.compression.CompressionRule.CollapseConsecutiveDuplicates
 import com.correx.core.tools.compression.CompressionRule.DropMatching
 import com.correx.core.tools.compression.CompressionRule.HeadTail
 import com.correx.core.tools.compression.CompressionRule.StripBlankLines
@@ -35,6 +36,7 @@ class DeclarativeCompressor(private val spec: OutputCompressionSpec) : ToolOutpu
             ?.let { regex -> lines.filterNot { regex.containsMatchIn(it) } }
             ?: lines
         is HeadTail -> applyHeadTail(rule, lines)
+        CollapseConsecutiveDuplicates -> collapseConsecutive(lines)
     }
 
     private fun applyHeadTail(rule: HeadTail, lines: List<String>): List<String> {
@@ -44,4 +46,25 @@ class DeclarativeCompressor(private val spec: OutputCompressionSpec) : ToolOutpu
             "… $elided lines elided …" +
             lines.takeLast(rule.tail)
     }
+
+    private fun collapseConsecutive(lines: List<String>): List<String> {
+        if (lines.isEmpty()) return lines
+        val out = ArrayList<String>(lines.size)
+        var prev = lines.first()
+        var count = 1
+        for (line in lines.drop(1)) {
+            if (line == prev) {
+                count++
+            } else {
+                out += render(prev, count)
+                prev = line
+                count = 1
+            }
+        }
+        out += render(prev, count)
+        return out
+    }
+
+    private fun render(line: String, count: Int): String =
+        if (count > 1) "$line (×$count)" else line
 }

core/tools/src/main/kotlin/com/correx/core/tools/compression/OutputCompressionSpec.kt

@@ -43,4 +43,13 @@ sealed interface CompressionRule {
     @Serializable
     @SerialName("head_tail")
     data class HeadTail(val head: Int, val tail: Int) : CompressionRule
+
+    /**
+     * Collapse runs of identical adjacent lines into a single line, appending an
+     * occurrence count (e.g. `Error: timeout (×14)`) when the run is longer than
+     * one. Order-preserving; never drops unique content — safe as a default.
+     */
+    @Serializable
+    @SerialName("collapse_consecutive_duplicates")
+    data object CollapseConsecutiveDuplicates : CompressionRule
 }

core/tools/src/test/kotlin/com/correx/core/tools/compression/DeclarativeCompressorTest.kt

@@ -1,5 +1,6 @@
 package com.correx.core.tools.compression
 
+import com.correx.core.tools.compression.CompressionRule.CollapseConsecutiveDuplicates
 import com.correx.core.tools.compression.CompressionRule.DropMatching
 import com.correx.core.tools.compression.CompressionRule.HeadTail
 import com.correx.core.tools.compression.CompressionRule.StripBlankLines
@@ -50,6 +51,20 @@ class DeclarativeCompressorTest {
         assertEquals(raw, out)
     }
 
+    @Test
+    fun `CollapseConsecutiveDuplicates collapses runs of identical adjacent lines with a count`() {
+        val raw = "Error: timeout\nError: timeout\nError: timeout\nok\nError: timeout"
+        val out = compress(OutputCompressionSpec(listOf(CollapseConsecutiveDuplicates)), raw)
+        assertEquals("Error: timeout (×3)\nok\nError: timeout", out)
+    }
+
+    @Test
+    fun `CollapseConsecutiveDuplicates leaves singletons and non-adjacent duplicates untouched`() {
+        val raw = "a\nb\na"
+        val out = compress(OutputCompressionSpec(listOf(CollapseConsecutiveDuplicates)), raw)
+        assertEquals(raw, out)
+    }
+
     @Test
     fun `read_file spec strips blanks then leading whitespace`() {
         val spec = OutputCompressionSpec(listOf(StripBlankLines, StripLeadingWhitespace))
@@ -102,7 +117,10 @@ class DeclarativeCompressorTest {
     @Test
     fun `spec round-trips through JSON with every rule variant (config-reachable)`() {
         val spec = OutputCompressionSpec(
-            rules = listOf(StripBlankLines, StripLeadingWhitespace, DropMatching("^Progress: "), HeadTail(3, 3)),
+            rules = listOf(
+                StripBlankLines, StripLeadingWhitespace, DropMatching("^Progress: "),
+                HeadTail(3, 3), CollapseConsecutiveDuplicates,
+            ),
             bypassOnError = false,
         )
         val encoded = Json.encodeToString(OutputCompressionSpec.serializer(), spec)