diff --git a/crates/aura-cli/tests/cli_run.rs b/crates/aura-cli/tests/cli_run.rs
index 13cb19a..c139755 100644
--- a/crates/aura-cli/tests/cli_run.rs
+++ b/crates/aura-cli/tests/cli_run.rs
@@ -5,7 +5,7 @@ use std::path::Path;
 use std::process::Command;
 
 mod common;
-use common::{fresh_project, fresh_project_with_data};
+use common::{fresh_project, fresh_project_with_data, fresh_project_with_gapped_data};
 
 /// Path to the freshly-built `aura` binary (Cargo sets this env var for the test
 /// crate; the binary is named `aura` in `Cargo.toml`).
@@ -5862,3 +5862,45 @@ fn shipped_r_meanrev_example_runs_end_to_end_via_aura_run() {
     assert!(stdout.contains("\"n_trades\":0"), "{stdout}");
     assert!(stdout.contains("\"total_pips\":0.0"), "{stdout}");
 }
+
+/// Property (#264, coverage cut 1): `aura data coverage <SYMBOL>` surfaces the
+/// archive's month COVERAGE from the monthly file index — the first and last
+/// present month AND every interior missing-month range (a gap) — so the Copper
+/// failure mode is visible up front. Copper had files from 2016-08 but was
+/// missing 2018-01..2018-10, so a first/last-bounds check passed while a
+/// window opening in the hole had no data, aborting a multi-hour campaign
+/// mid-run; a per-symbol gap report would have caught it before the run. Over a
+/// hermetic synthetic archive whose `GAPSYM` has 2024-01..02 and 2024-05..06
+/// present and 2024-03..04 absent, the verb exits 0, frames the span by its
+/// first (2024-01) and last (2024-06) present month, and reports the interior
+/// hole as a single collapsed month-range line `missing: 2024-03..2024-04`
+/// (one line for the whole contiguous gap, as Copper's ten-month hole would be
+/// one line — not one line per missing month).
+#[test]
+fn data_coverage_reports_month_span_and_interior_gap_range() {
+    let (cwd, _g) = fresh_project_with_gapped_data();
+    let out = std::process::Command::new(env!("CARGO_BIN_EXE_aura"))
+        .args(["data", "coverage", "GAPSYM"])
+        .current_dir(&cwd)
+        .output()
+        .expect("spawn aura data coverage");
+    assert_eq!(
+        out.status.code(),
+        Some(0),
+        "exit: {:?}, stderr: {}",
+        out.status,
+        String::from_utf8_lossy(&out.stderr)
+    );
+    let stdout = String::from_utf8(out.stdout).expect("utf-8 stdout");
+    // The interior gap is the headline — the Copper failure the verb exists to
+    // surface — reported as one collapsed range for the whole contiguous hole.
+    assert!(
+        stdout.contains("missing: 2024-03..2024-04"),
+        "interior gap month-range reported as one line: {stdout}"
+    );
+    // The span bounds frame the gap: first and last present month.
+    assert!(
+        stdout.contains("2024-01") && stdout.contains("2024-06"),
+        "first (2024-01) and last (2024-06) present month reported: {stdout}"
+    );
+}
diff --git a/crates/aura-cli/tests/common/mod.rs b/crates/aura-cli/tests/common/mod.rs
index ad139ff..8b3697b 100644
--- a/crates/aura-cli/tests/common/mod.rs
+++ b/crates/aura-cli/tests/common/mod.rs
@@ -127,6 +127,26 @@ pub fn fresh_project_with_data() -> (PathBuf, FreshProject) {
     (root.clone(), FreshProject { root })
 }
 
+/// Like [`fresh_project_with_data`], but the single symbol `GAPSYM` carries a
+/// DELIBERATE interior month gap: monthly files exist for 2024-01..2024-02 and
+/// 2024-05..2024-06, while 2024-03..2024-04 are absent. This is the Copper
+/// failure shape (#264 — files present at both ends while an interior window
+/// has no data, so a first/last-bounds check passes but a campaign aborts
+/// mid-run). For tests whose property is per-symbol month-gap reporting: the
+/// two `write_symbol_archive` calls write disjoint contiguous segments into the
+/// same `data/` dir (the second re-writes GAPSYM's identical geometry sidecar),
+/// leaving March and April as a real hole in the monthly file index.
+#[allow(dead_code)]
+pub fn fresh_project_with_gapped_data() -> (PathBuf, FreshProject) {
+    let root = mint_tempdir();
+    write_project_files(&root, Some("data"));
+    let data_dir = root.join("data");
+    std::fs::create_dir_all(&data_dir).expect("create synthetic gapped archive dir");
+    synthetic_data::write_symbol_archive(&data_dir, "GAPSYM", (2024, 1), (2024, 2));
+    synthetic_data::write_symbol_archive(&data_dir, "GAPSYM", (2024, 5), (2024, 6));
+    (root.clone(), FreshProject { root })
+}
+
 /// A scratch filesystem entry a test writes under the git-tracked
 /// demo-project fixture root (only `runs/` there is fixture-gitignored),
 /// removed on drop — including during a mid-test panic — so a failed