diff --git a/core/toolintent/src/main/kotlin/com/correx/core/toolintent/rules/WriteScopeRule.kt b/core/toolintent/src/main/kotlin/com/correx/core/toolintent/rules/WriteScopeRule.kt
new file mode 100644
index 00000000..85dd7438
--- /dev/null
+++ b/core/toolintent/src/main/kotlin/com/correx/core/toolintent/rules/WriteScopeRule.kt
@@ -0,0 +1,72 @@
+package com.correx.core.toolintent.rules
+
+import com.correx.core.events.events.ToolCallObservation
+import com.correx.core.events.risk.RiskAction
+import com.correx.core.toolintent.ToolCallAssessment
+import com.correx.core.toolintent.ToolCallAssessmentInput
+import com.correx.core.toolintent.ToolCallRule
+import com.correx.core.toolintent.maxAction
+import com.correx.core.tools.contract.ToolCapability
+import com.correx.core.validation.model.ValidationIssue
+import com.correx.core.validation.model.ValidationSeverity
+import java.nio.file.FileSystems
+import java.nio.file.Path
+
+/**
+ * Write-scope adherence. When the session has claimed a task that declared affected_paths, an
+ * in-workspace write outside that scope is BLOCKED — but **declarably**: the message tells the
+ * agent that if the change is genuinely needed (a dependency, a caller the plan didn't foresee) it
+ * should widen the task's affected_paths via task_update (which re-records the scope), then retry.
+ * So legitimate work is never trapped — only forced to be explicit, turning silent scope-creep into
+ * a recorded, auditable scope change. No active task or no declared scope ⇒ nothing to enforce;
+ * out-of-workspace targets are PathContainmentRule's concern.
+ */
+class WriteScopeRule : ToolCallRule {
+
+    override fun appliesTo(capabilities: Set<ToolCapability>): Boolean =
+        ToolCapability.FILE_WRITE in capabilities
+
+    override fun assess(input: ToolCallAssessmentInput): ToolCallAssessment {
+        val active = input.session.activeTask
+        if (active == null || active.scope.isEmpty()) return ToolCallAssessment()
+
+        val workspaceReal = input.probe.resolveReal(input.workspace.workspaceRoot)
+        val matchers = active.scope.map { FileSystems.getDefault().getPathMatcher("glob:${it.removePrefix("./")}") }
+
+        val issues = mutableListOf<ValidationIssue>()
+        val observations = mutableListOf<ToolCallObservation>()
+        var disposition = RiskAction.PROCEED
+
+        for (raw in candidatePathStrings(input.paramRoles, input.request.parameters)) {
+            val candidate = Path.of(raw)
+            val resolvedReal = input.probe.resolveReal(
+                if (candidate.isAbsolute) candidate else input.workspace.workspaceRoot.resolve(candidate),
+            )
+            if (!resolvedReal.startsWith(workspaceReal)) continue // out of workspace: not this gate
+            val rel = workspaceReal.relativize(resolvedReal)
+            val inScope = matchers.any { it.matches(rel) }
+
+            observations += ToolCallObservation(
+                ruleCode = RULE_CODE,
+                facts = mapOf("path" to raw, "inScope" to inScope.toString(), "task" to active.taskId),
+            )
+
+            if (!inScope) {
+                issues += ValidationIssue(
+                    code = RULE_CODE,
+                    message = "Tool '${input.request.toolName}' writes '$raw', outside claimed task " +
+                        "${active.taskId}'s affected_paths (${active.scope}). If this change is needed, " +
+                        "add its path via task_update affected_paths (note why), then retry.",
+                    severity = ValidationSeverity.ERROR,
+                )
+                disposition = maxAction(disposition, RiskAction.BLOCK)
+            }
+        }
+
+        return ToolCallAssessment(issues = issues, observations = observations, disposition = disposition)
+    }
+
+    private companion object {
+        const val RULE_CODE = "WRITE_SCOPE"
+    }
+}
diff --git a/core/toolintent/src/test/kotlin/com/correx/core/toolintent/WriteScopeRuleTest.kt b/core/toolintent/src/test/kotlin/com/correx/core/toolintent/WriteScopeRuleTest.kt
new file mode 100644
index 00000000..63389229
--- /dev/null
+++ b/core/toolintent/src/test/kotlin/com/correx/core/toolintent/WriteScopeRuleTest.kt
@@ -0,0 +1,55 @@
+package com.correx.core.toolintent
+
+import com.correx.core.events.events.ToolRequest
+import com.correx.core.events.risk.RiskAction
+import com.correx.core.events.types.SessionId
+import com.correx.core.events.types.StageId
+import com.correx.core.events.types.ToolInvocationId
+import com.correx.core.toolintent.rules.WriteScopeRule
+import com.correx.core.tools.contract.ToolCapability
+import java.nio.file.Path
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class WriteScopeRuleTest {
+
+    private val workspace = Path.of("/work/project")
+    private val rule = WriteScopeRule()
+
+    private class FakeProbe : WorldProbe {
+        override fun exists(path: Path) = true
+        override fun resolveReal(path: Path): Path = path.toAbsolutePath().normalize()
+    }
+
+    private fun input(pathArg: String, active: ActiveTask?) = ToolCallAssessmentInput(
+        request = ToolRequest(ToolInvocationId("i"), SessionId("s"), StageId("st"), "file_write", mapOf("path" to pathArg)),
+        capabilities = setOf(ToolCapability.FILE_WRITE),
+        workspace = WorkspacePolicy(workspace, emptyList()),
+        probe = FakeProbe(),
+        session = SessionContext(activeTask = active),
+    )
+
+    private val scoped = ActiveTask("auth-2", listOf("core/auth/**"))
+
+    @Test
+    fun `no active task means nothing to enforce`() {
+        assertEquals(RiskAction.PROCEED, rule.assess(input("/work/project/core/billing/X.kt", active = null)).disposition)
+    }
+
+    @Test
+    fun `a write inside the claimed task scope proceeds`() {
+        val r = rule.assess(input("/work/project/core/auth/Login.kt", scoped))
+        assertEquals(RiskAction.PROCEED, r.disposition)
+        assertEquals("true", r.observations.single().facts["inScope"])
+    }
+
+    @Test
+    fun `a write outside the claimed task scope is blocked and names the task`() {
+        val r = rule.assess(input("/work/project/core/billing/Charge.kt", scoped))
+        assertEquals(RiskAction.BLOCK, r.disposition)
+        assertEquals("WRITE_SCOPE", r.issues.single().code)
+        assertTrue(r.issues.single().message.contains("auth-2"))
+        assertTrue(r.issues.single().message.contains("task_update affected_paths"))
+    }
+}