diff --git a/Cargo.toml b/Cargo.toml
index b5b305b..0b8fcc3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,7 @@ members = [
     "common",
     "server",
     "client",
+    "testing",
 ]
 resolver = "3"
 
diff --git a/Jenkinsfile b/Jenkinsfile
index 70334bd..29a9b92 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -28,9 +28,7 @@ pipeline {
 
     stage('Format') {
       steps {
-        sh 'cargo fmt --all --manifest-path common/Cargo.toml -- --check'
-        sh 'cargo fmt --all --manifest-path server/Cargo.toml -- --check'
-        sh 'cargo fmt --all --manifest-path client/Cargo.toml -- --check'
+        sh 'cargo fmt --all -- --check'
       }
     }
 
@@ -40,6 +38,12 @@ pipeline {
       }
     }
 
+    stage('Testing') {
+      steps {
+        sh 'cargo test -p lesavka_testing'
+      }
+    }
+
     stage('Quality Gate') {
       steps {
         sh 'QUALITY_GATE_PUSHGATEWAY_URL="${QUALITY_GATE_PUSHGATEWAY_URL}" scripts/ci/quality_gate.sh'
diff --git a/client/src/lib.rs b/client/src/lib.rs
index 018300b..1ab479d 100644
--- a/client/src/lib.rs
+++ b/client/src/lib.rs
@@ -10,7 +10,4 @@ pub mod layout;
 pub mod output;
 pub mod paste;
 
-#[cfg(test)]
-mod tests;
-
 pub use app::LesavkaClientApp;
diff --git a/client/src/tests/integration_test.rs b/client/src/tests/integration_test.rs
deleted file mode 100644
index 30767d9..0000000
--- a/client/src/tests/integration_test.rs
+++ /dev/null
@@ -1,19 +0,0 @@
-// client/tests/integration.rs
-
-mod tests {
-    use crate::input::keymap::{char_to_usage, is_modifier, keycode_to_usage};
-    use evdev::KeyCode;
-
-    #[test]
-    fn keymap_smoke_test_hits_letter_number_modifier_and_char_paths() {
-        assert_eq!(keycode_to_usage(KeyCode::KEY_A), Some(0x04));
-        assert_eq!(keycode_to_usage(KeyCode::KEY_Z), Some(0x1D));
-        assert_eq!(keycode_to_usage(KeyCode::KEY_F1), Some(0x3A));
-        assert_eq!(keycode_to_usage(KeyCode::KEY_KPENTER), Some(0x58));
-        assert_eq!(keycode_to_usage(KeyCode::KEY_LEFTCTRL), None);
-        assert!(is_modifier(KeyCode::KEY_LEFTCTRL).is_some());
-        assert!(is_modifier(KeyCode::KEY_RIGHTMETA).is_some());
-        assert_eq!(char_to_usage('!'), Some((0x1E, 0x02)));
-        assert_eq!(char_to_usage(' '), Some((0x2C, 0x00)));
-    }
-}
diff --git a/client/src/tests/mod.rs b/client/src/tests/mod.rs
deleted file mode 100644
index 13764c8..0000000
--- a/client/src/tests/mod.rs
+++ /dev/null
@@ -1,3 +0,0 @@
-// client/src/tests/mod.rs
-
-pub mod integration_test;
diff --git a/scripts/ci/hygiene_gate.sh b/scripts/ci/hygiene_gate.sh
index f5bd758..fbe9dac 100755
--- a/scripts/ci/hygiene_gate.sh
+++ b/scripts/ci/hygiene_gate.sh
@@ -16,7 +16,7 @@ import json
 import pathlib
 import re
 import sys
-from collections import Counter, defaultdict
+from collections import defaultdict
 
 clippy_path = pathlib.Path(sys.argv[1])
 baseline_path = pathlib.Path(sys.argv[2])
@@ -126,6 +126,54 @@ def source_loc_counts() -> dict[str, int]:
         counts[rel] = sum(1 for _ in file.open('r', encoding='utf-8'))
     return dict(sorted(counts.items()))
 
+def integration_layout_violations() -> list[str]:
+    violations: list[str] = []
+    for file in sorted(root.rglob('*.rs')):
+        rel = repo_relative(str(file))
+        if rel is None or rel.startswith('target/') or rel.startswith('testing/'):
+            continue
+        parts = pathlib.Path(rel).parts
+        if len(parts) >= 3 and parts[1] == 'src' and parts[2] == 'tests':
+            violations.append(
+                f'{rel}: integration tests must live under testing/tests/ instead of package-local src/tests/'
+            )
+        elif len(parts) >= 2 and parts[1] == 'tests':
+            violations.append(
+                f'{rel}: integration tests must live under testing/tests/ instead of package-local tests/'
+            )
+    return violations
+
+def testing_contract_violations() -> list[str]:
+    violations: list[str] = []
+    contract_dir = root / 'testing' / 'tests'
+    if not contract_dir.exists():
+        return ['testing/tests: missing dedicated top-level integration test directory']
+
+    test_files = sorted(contract_dir.rglob('*.rs'))
+    if not test_files:
+        return ['testing/tests: no integration test files found']
+
+    filename_re = re.compile(r'^[a-z0-9_]+\.rs$')
+    required_markers = ('Scope:', 'Targets:', 'Why:')
+    for file in test_files:
+        rel = repo_relative(str(file))
+        if rel is None:
+            continue
+        loc = sum(1 for _ in file.open('r', encoding='utf-8'))
+        if loc > 500:
+            violations.append(f'{rel}: exceeds 500 LOC contract ({loc})')
+        if not filename_re.match(file.name):
+            violations.append(f'{rel}: filename must use snake_case for meaningful modularization')
+
+        text = file.read_text(encoding='utf-8')
+        header = '\n'.join(text.splitlines()[:20])
+        for marker in required_markers:
+            if marker not in header:
+                violations.append(f'{rel}: missing required module contract marker {marker}')
+        if '#[test]' not in text and '#[tokio::test]' not in text:
+            violations.append(f'{rel}: missing test entrypoints')
+    return violations
+
 current = {}
 for path, loc in source_loc_counts().items():
     current[path] = {'loc': loc}
@@ -154,6 +202,9 @@ for path, current_entry in current.items():
                 f'{path}: {key} grew from {baseline_value} to {current_value}'
             )
 
+layout_violations = integration_layout_violations()
+testing_violations = testing_contract_violations()
+
 totals = {
     'files': len(current),
     'over_500': sum(1 for entry in current.values() if int(entry.get('loc', 0)) > 500),
@@ -167,6 +218,8 @@ lines.append(f"files tracked: {totals['files']}")
 lines.append(f"files over 500 LOC: {totals['over_500']}")
 lines.append(f"clippy warnings tracked: {totals['clippy_warnings']}")
 lines.append(f"non-trivial undocumented functions tracked: {totals['doc_debt']}")
+lines.append(f'legacy integration-test layout violations: {len(layout_violations)}')
+lines.append(f'testing module contract violations: {len(testing_violations)}')
 lines.append('')
 lines.append('path | loc | clippy warnings | doc debt | baseline status')
 lines.append('-' * 78)
@@ -193,11 +246,27 @@ for path in sorted(current):
         f"{path} | {entry.get('loc', 0)} | {entry.get('clippy_warnings', 0)} | {entry.get('doc_debt', 0)} | {baseline_loc}/{baseline_clippy}/{baseline_doc} | {status}"
     )
 
+if layout_violations:
+    lines.append('')
+    lines.append('layout violations')
+    lines.append('-' * 78)
+    lines.extend(layout_violations)
+
+if testing_violations:
+    lines.append('')
+    lines.append('testing module contract violations')
+    lines.append('-' * 78)
+    lines.extend(testing_violations)
+
 summary_path.write_text('\n'.join(lines) + '\n', encoding='utf-8')
 print(summary_path.read_text(encoding='utf-8'))
 
-if regressions:
+if regressions or layout_violations or testing_violations:
     for line in regressions:
         print(line, file=sys.stderr)
+    for line in layout_violations:
+        print(line, file=sys.stderr)
+    for line in testing_violations:
+        print(line, file=sys.stderr)
     raise SystemExit(1)
 PY
diff --git a/scripts/ci/hygiene_gate_baseline.json b/scripts/ci/hygiene_gate_baseline.json
index 553a1eb..4fc7867 100644
--- a/scripts/ci/hygiene_gate_baseline.json
+++ b/scripts/ci/hygiene_gate_baseline.json
@@ -186,6 +186,10 @@
       "loc": 236,
       "clippy_warnings": 8,
       "doc_debt": 6
+    },
+    "testing/src/lib.rs": {
+      "loc": 10,
+      "doc_debt": 0
     }
   }
 }
diff --git a/scripts/ci/quality_gate.sh b/scripts/ci/quality_gate.sh
index d42a3f7..12e1fce 100755
--- a/scripts/ci/quality_gate.sh
+++ b/scripts/ci/quality_gate.sh
@@ -7,6 +7,7 @@ COVERAGE_JSON="${REPORT_DIR}/coverage.json"
 SUMMARY_TXT="${REPORT_DIR}/summary.txt"
 METRICS_FILE="${REPORT_DIR}/metrics.prom"
 BASELINE_JSON="${ROOT_DIR}/scripts/ci/quality_gate_baseline.json"
+COVERAGE_CONTRACT_JSON="${ROOT_DIR}/testing/coverage_contract.json"
 PUSHGATEWAY_URL=${QUALITY_GATE_PUSHGATEWAY_URL:-}
 
 mkdir -p "${REPORT_DIR}"
@@ -82,7 +83,7 @@ publish_metrics() {
 
 status=0
 if cargo llvm-cov --workspace --all-targets --summary-only --json --output-path "${COVERAGE_JSON}"; then
-  if python3 - "${COVERAGE_JSON}" "${BASELINE_JSON}" "${METRICS_FILE}" "${SUMMARY_TXT}" "${ROOT_DIR}" <<'PY'
+  if python3 - "${COVERAGE_JSON}" "${BASELINE_JSON}" "${METRICS_FILE}" "${SUMMARY_TXT}" "${ROOT_DIR}" "${COVERAGE_CONTRACT_JSON}" <<'PY'
 import json
 import pathlib
 import sys
@@ -93,6 +94,7 @@ baseline_path = pathlib.Path(sys.argv[2])
 metrics_path = pathlib.Path(sys.argv[3])
 summary_path = pathlib.Path(sys.argv[4])
 root = pathlib.Path(sys.argv[5])
+contract_path = pathlib.Path(sys.argv[6])
 
 with coverage_path.open('r', encoding='utf-8') as fh:
     report = json.load(fh)
@@ -138,6 +140,29 @@ for path, current in current_by_path.items():
             f"{path}: line coverage fell from {baseline_entry['line_percent']:.2f}% to {current['line_percent']:.2f}%"
         )
 
+coverage_contract = {'minimum_line_percent': 95.0, 'files': []}
+if contract_path.exists():
+    with contract_path.open('r', encoding='utf-8') as fh:
+        coverage_contract = json.load(fh)
+
+contract_min = float(coverage_contract.get('minimum_line_percent', 95.0))
+contract_files = list(dict.fromkeys(coverage_contract.get('files', [])))
+contract_failures = []
+contract_files_at_target = 0
+for path in contract_files:
+    current = current_by_path.get(path)
+    if current is None:
+        contract_failures.append(f'{path}: missing from coverage report')
+        continue
+    if current['line_percent'] + 0.01 < contract_min:
+        contract_failures.append(
+            f'{path}: contract requires >= {contract_min:.2f}% line coverage, found {current["line_percent"]:.2f}%'
+        )
+    else:
+        contract_files_at_target += 1
+    if current['loc'] > 500:
+        contract_failures.append(f'{path}: contract requires <= 500 LOC, found {current["loc"]}')
+
 workspace_lines = float(coverage_totals['lines']['percent'])
 files_at_95 = sum(1 for item in files if item['line_percent'] >= 95.0)
 files_below_95 = len(files) - files_at_95
@@ -146,7 +171,7 @@ over_500 = sum(1 for item in files if item['loc'] > 500)
 metrics = []
 metrics.append('# HELP platform_quality_gate_runs_total Number of quality gate runs by result.')
 metrics.append('# TYPE platform_quality_gate_runs_total counter')
-status_label = 'ok' if not regressions and not missing_from_baseline else 'failed'
+status_label = 'ok' if not regressions and not missing_from_baseline and not contract_failures else 'failed'
 metrics.append(f'platform_quality_gate_runs_total{{suite="lesavka",status="{status_label}"}} 1')
 metrics.append('# HELP platform_quality_gate_workspace_line_coverage_percent Workspace line coverage percent.')
 metrics.append('# TYPE platform_quality_gate_workspace_line_coverage_percent gauge')
@@ -163,6 +188,17 @@ metrics.append(f'platform_quality_gate_files_below_95_total{{suite="lesavka"}} {
 metrics.append('# HELP platform_quality_gate_source_lines_over_500_total Count of tracked source files over 500 LOC.')
 metrics.append('# TYPE platform_quality_gate_source_lines_over_500_total gauge')
 metrics.append(f'platform_quality_gate_source_lines_over_500_total{{suite="lesavka"}} {over_500}')
+metrics.append('# HELP platform_quality_gate_contract_files_total Count of files covered by the strict testing coverage contract.')
+metrics.append('# TYPE platform_quality_gate_contract_files_total gauge')
+metrics.append(f'platform_quality_gate_contract_files_total{{suite="lesavka"}} {len(contract_files)}')
+metrics.append('# HELP platform_quality_gate_contract_files_at_target_total Count of strict contract files meeting the line coverage target.')
+metrics.append('# TYPE platform_quality_gate_contract_files_at_target_total gauge')
+metrics.append(f'platform_quality_gate_contract_files_at_target_total{{suite="lesavka"}} {contract_files_at_target}')
+metrics.append('# HELP platform_quality_gate_contract_files_below_target_total Count of strict contract files missing the line coverage target or LOC cap.')
+metrics.append('# TYPE platform_quality_gate_contract_files_below_target_total gauge')
+metrics.append(
+    f'platform_quality_gate_contract_files_below_target_total{{suite="lesavka"}} {len(contract_failures)}'
+)
 metrics.append('# HELP platform_quality_gate_file_line_coverage_percent Per-file line coverage percent.')
 metrics.append('# TYPE platform_quality_gate_file_line_coverage_percent gauge')
 metrics.append('# HELP platform_quality_gate_file_source_lines Per-file source line count.')
@@ -189,6 +225,7 @@ lines.append(f'source files tracked: {len(files)}')
 lines.append(f'files >= 95% line coverage: {files_at_95}')
 lines.append(f'files < 95% line coverage: {files_below_95}')
 lines.append(f'files over 500 LOC: {over_500}')
+lines.append(f'strict contract files at target: {contract_files_at_target}/{len(contract_files)} (>= {contract_min:.2f}% and <= 500 LOC)')
 lines.append('')
 lines.append('path | loc | line coverage | baseline loc | baseline coverage | status')
 lines.append('-' * 86)
@@ -208,6 +245,17 @@ for item in files:
         f"{item['path']} | {item['loc']} | {item['line_percent']:.2f}% | {baseline_loc} | {baseline_cov} | {status}"
     )
 
+if contract_files:
+    lines.append('')
+    lines.append('strict testing coverage contract')
+    lines.append('-' * 86)
+    for path in contract_files:
+        current = current_by_path.get(path)
+        if current is None:
+            lines.append(f'{path} | missing')
+        else:
+            lines.append(f'{path} | {current["loc"]} LOC | {current["line_percent"]:.2f}%')
+
 summary_path.write_text('\n'.join(lines) + '\n', encoding='utf-8')
 
 print(summary_path.read_text(encoding='utf-8'))
@@ -215,9 +263,11 @@ print(summary_path.read_text(encoding='utf-8'))
 if missing_from_baseline:
     print('missing baseline entries:', ', '.join(missing_from_baseline), file=sys.stderr)
 
-if regressions or missing_from_baseline:
+if regressions or missing_from_baseline or contract_failures:
     for line in regressions:
         print(line, file=sys.stderr)
+    for line in contract_failures:
+        print(line, file=sys.stderr)
     raise SystemExit(1)
 PY
   then
diff --git a/testing/Cargo.toml b/testing/Cargo.toml
new file mode 100644
index 0000000..5bcdc0f
--- /dev/null
+++ b/testing/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+name = "lesavka_testing"
+version = "0.1.0"
+edition = "2024"
+publish = false
+
+[lib]
+name = "lesavka_testing"
+path = "src/lib.rs"
+
+[dev-dependencies]
+evdev = "0.13"
+libc = "0.2"
+lesavka_client = { path = "../client" }
+lesavka_common = { path = "../common" }
+lesavka_server = { path = "../server" }
diff --git a/testing/coverage_contract.json b/testing/coverage_contract.json
new file mode 100644
index 0000000..cc2ff31
--- /dev/null
+++ b/testing/coverage_contract.json
@@ -0,0 +1,10 @@
+{
+  "minimum_line_percent": 95.0,
+  "files": [
+    "client/src/app_support.rs",
+    "client/src/input/keymap.rs",
+    "common/src/hid.rs",
+    "common/src/paste.rs",
+    "server/src/paste.rs"
+  ]
+}
diff --git a/testing/src/lib.rs b/testing/src/lib.rs
new file mode 100644
index 0000000..5a8a51d
--- /dev/null
+++ b/testing/src/lib.rs
@@ -0,0 +1,10 @@
+//! Top-level integration testing crate for the lesavka workspace.
+//!
+//! Scope: keep cross-crate and contract-style tests out of package-local
+//! `src/tests` and `tests` folders so CI has one integration test entrypoint.
+//! Targets: the `testing/tests` suite plus coverage contracts consumed by the
+//! Jenkins quality gate.
+//! Why: a single top-level testing module is easier to scale, review, and
+//! ratchet than ad-hoc integration tests spread across workspace members.
+
+#![forbid(unsafe_code)]
diff --git a/testing/tests/client_keymap_contract.rs b/testing/tests/client_keymap_contract.rs
new file mode 100644
index 0000000..57931a2
--- /dev/null
+++ b/testing/tests/client_keymap_contract.rs
@@ -0,0 +1,161 @@
+//! Integration coverage for the client HID keymap contract.
+//!
+//! Scope: exercise the public keycode and modifier helpers through the
+//! top-level testing crate instead of package-local integration tests.
+//! Targets: `client/src/input/keymap.rs` and its shared-character delegation.
+//! Why: the full keyboard map is large enough that one dedicated contract test
+//! is clearer than scattering smoke coverage across unrelated crates.
+
+use evdev::KeyCode;
+use lesavka_client::input::keymap::{char_to_usage, is_modifier, keycode_to_usage};
+
+#[test]
+fn keycode_to_usage_covers_each_supported_keyboard_block() {
+    let cases = [
+        (KeyCode::KEY_A, 0x04),
+        (KeyCode::KEY_B, 0x05),
+        (KeyCode::KEY_C, 0x06),
+        (KeyCode::KEY_D, 0x07),
+        (KeyCode::KEY_E, 0x08),
+        (KeyCode::KEY_F, 0x09),
+        (KeyCode::KEY_G, 0x0A),
+        (KeyCode::KEY_H, 0x0B),
+        (KeyCode::KEY_I, 0x0C),
+        (KeyCode::KEY_J, 0x0D),
+        (KeyCode::KEY_K, 0x0E),
+        (KeyCode::KEY_L, 0x0F),
+        (KeyCode::KEY_M, 0x10),
+        (KeyCode::KEY_N, 0x11),
+        (KeyCode::KEY_O, 0x12),
+        (KeyCode::KEY_P, 0x13),
+        (KeyCode::KEY_Q, 0x14),
+        (KeyCode::KEY_R, 0x15),
+        (KeyCode::KEY_S, 0x16),
+        (KeyCode::KEY_T, 0x17),
+        (KeyCode::KEY_U, 0x18),
+        (KeyCode::KEY_V, 0x19),
+        (KeyCode::KEY_W, 0x1A),
+        (KeyCode::KEY_X, 0x1B),
+        (KeyCode::KEY_Y, 0x1C),
+        (KeyCode::KEY_Z, 0x1D),
+        (KeyCode::KEY_1, 0x1E),
+        (KeyCode::KEY_2, 0x1F),
+        (KeyCode::KEY_3, 0x20),
+        (KeyCode::KEY_4, 0x21),
+        (KeyCode::KEY_5, 0x22),
+        (KeyCode::KEY_6, 0x23),
+        (KeyCode::KEY_7, 0x24),
+        (KeyCode::KEY_8, 0x25),
+        (KeyCode::KEY_9, 0x26),
+        (KeyCode::KEY_0, 0x27),
+        (KeyCode::KEY_ENTER, 0x28),
+        (KeyCode::KEY_ESC, 0x29),
+        (KeyCode::KEY_BACKSPACE, 0x2A),
+        (KeyCode::KEY_TAB, 0x2B),
+        (KeyCode::KEY_SPACE, 0x2C),
+        (KeyCode::KEY_MINUS, 0x2D),
+        (KeyCode::KEY_EQUAL, 0x2E),
+        (KeyCode::KEY_LEFTBRACE, 0x2F),
+        (KeyCode::KEY_RIGHTBRACE, 0x30),
+        (KeyCode::KEY_BACKSLASH, 0x31),
+        (KeyCode::KEY_SEMICOLON, 0x33),
+        (KeyCode::KEY_APOSTROPHE, 0x34),
+        (KeyCode::KEY_GRAVE, 0x35),
+        (KeyCode::KEY_COMMA, 0x36),
+        (KeyCode::KEY_DOT, 0x37),
+        (KeyCode::KEY_SLASH, 0x38),
+        (KeyCode::KEY_CAPSLOCK, 0x39),
+        (KeyCode::KEY_F1, 0x3A),
+        (KeyCode::KEY_F2, 0x3B),
+        (KeyCode::KEY_F3, 0x3C),
+        (KeyCode::KEY_F4, 0x3D),
+        (KeyCode::KEY_F5, 0x3E),
+        (KeyCode::KEY_F6, 0x3F),
+        (KeyCode::KEY_F7, 0x40),
+        (KeyCode::KEY_F8, 0x41),
+        (KeyCode::KEY_F9, 0x42),
+        (KeyCode::KEY_F10, 0x43),
+        (KeyCode::KEY_F11, 0x44),
+        (KeyCode::KEY_F12, 0x45),
+        (KeyCode::KEY_SYSRQ, 0x46),
+        (KeyCode::KEY_SCROLLLOCK, 0x47),
+        (KeyCode::KEY_PAUSE, 0x48),
+        (KeyCode::KEY_INSERT, 0x49),
+        (KeyCode::KEY_HOME, 0x4A),
+        (KeyCode::KEY_PAGEUP, 0x4B),
+        (KeyCode::KEY_DELETE, 0x4C),
+        (KeyCode::KEY_END, 0x4D),
+        (KeyCode::KEY_PAGEDOWN, 0x4E),
+        (KeyCode::KEY_RIGHT, 0x4F),
+        (KeyCode::KEY_LEFT, 0x50),
+        (KeyCode::KEY_DOWN, 0x51),
+        (KeyCode::KEY_UP, 0x52),
+        (KeyCode::KEY_NUMLOCK, 0x53),
+        (KeyCode::KEY_KPSLASH, 0x54),
+        (KeyCode::KEY_KPASTERISK, 0x55),
+        (KeyCode::KEY_KPMINUS, 0x56),
+        (KeyCode::KEY_KPPLUS, 0x57),
+        (KeyCode::KEY_KPENTER, 0x58),
+        (KeyCode::KEY_KP1, 0x59),
+        (KeyCode::KEY_KP2, 0x5A),
+        (KeyCode::KEY_KP3, 0x5B),
+        (KeyCode::KEY_KP4, 0x5C),
+        (KeyCode::KEY_KP5, 0x5D),
+        (KeyCode::KEY_KP6, 0x5E),
+        (KeyCode::KEY_KP7, 0x5F),
+        (KeyCode::KEY_KP8, 0x60),
+        (KeyCode::KEY_KP9, 0x61),
+        (KeyCode::KEY_KP0, 0x62),
+        (KeyCode::KEY_KPDOT, 0x63),
+        (KeyCode::KEY_KPEQUAL, 0x67),
+        (KeyCode::KEY_102ND, 0x64),
+        (KeyCode::KEY_MENU, 0x65),
+    ];
+
+    for (key, usage) in cases {
+        assert_eq!(
+            keycode_to_usage(key),
+            Some(usage),
+            "unexpected mapping for {key:?}"
+        );
+    }
+
+    assert_eq!(keycode_to_usage(KeyCode::KEY_LEFTCTRL), None);
+    assert_eq!(keycode_to_usage(KeyCode::KEY_RESERVED), None);
+}
+
+#[test]
+fn is_modifier_covers_each_supported_modifier_bit() {
+    let cases = [
+        (KeyCode::KEY_LEFTCTRL, 0x01),
+        (KeyCode::KEY_LEFTSHIFT, 0x02),
+        (KeyCode::KEY_LEFTALT, 0x04),
+        (KeyCode::KEY_LEFTMETA, 0x08),
+        (KeyCode::KEY_RIGHTCTRL, 0x10),
+        (KeyCode::KEY_RIGHTSHIFT, 0x20),
+        (KeyCode::KEY_RIGHTALT, 0x40),
+        (KeyCode::KEY_RIGHTMETA, 0x80),
+    ];
+
+    for (key, mask) in cases {
+        assert_eq!(
+            is_modifier(key),
+            Some(mask),
+            "unexpected modifier for {key:?}"
+        );
+    }
+
+    assert_eq!(is_modifier(KeyCode::KEY_A), None);
+}
+
+#[test]
+fn char_to_usage_exposes_shared_hid_mapping_from_the_client_surface() {
+    assert_eq!(char_to_usage('a'), Some((0x04, 0x00)));
+    assert_eq!(char_to_usage('A'), Some((0x04, 0x02)));
+    assert_eq!(char_to_usage('0'), Some((0x27, 0x00)));
+    assert_eq!(char_to_usage('!'), Some((0x1E, 0x02)));
+    assert_eq!(char_to_usage('?'), Some((0x38, 0x02)));
+    assert_eq!(char_to_usage('\t'), Some((0x2B, 0x00)));
+    assert_eq!(char_to_usage('\n'), Some((0x28, 0x00)));
+    assert_eq!(char_to_usage('é'), None);
+}
diff --git a/server/tests/hid.rs b/testing/tests/server_runtime_contract.rs
similarity index 55%
rename from server/tests/hid.rs
rename to testing/tests/server_runtime_contract.rs
index 6dcc8a6..fb489fa 100644
--- a/server/tests/hid.rs
+++ b/testing/tests/server_runtime_contract.rs
@@ -1,3 +1,11 @@
+//! Integration coverage for public server runtime helpers.
+//!
+//! Scope: keep public helper smoke tests in the shared top-level testing
+//! module rather than the server crate's local `tests/` folder.
+//! Targets: `server/src/runtime_support.rs` public pure helpers.
+//! Why: these helpers are part of a cross-crate contract surface and fit the
+//! centralized testing layout better than package-scoped integration tests.
+
 use lesavka_server::runtime_support::{next_stream_id, should_recover_hid_error};
 
 #[test]
diff --git a/testing/tests/shared_hid_contract.rs b/testing/tests/shared_hid_contract.rs
new file mode 100644
index 0000000..b5045e8
--- /dev/null
+++ b/testing/tests/shared_hid_contract.rs
@@ -0,0 +1,79 @@
+//! Integration coverage for the shared printable-character HID contract.
+//!
+//! Scope: verify the shared character-to-HID table from the top-level testing
+//! module so both client and server rely on the same canonical assertions.
+//! Targets: `common/src/hid.rs`.
+//! Why: this mapping is a cross-crate contract and should live in one obvious
+//! place instead of being duplicated by package-local test suites.
+
+use lesavka_common::hid::char_to_usage;
+
+#[test]
+fn char_to_usage_covers_letters_digits_symbols_and_whitespace() {
+    for (offset, ch) in ('a'..='z').enumerate() {
+        assert_eq!(char_to_usage(ch), Some((0x04 + offset as u8, 0x00)));
+    }
+
+    for (offset, ch) in ('A'..='Z').enumerate() {
+        assert_eq!(char_to_usage(ch), Some((0x04 + offset as u8, 0x02)));
+    }
+
+    for (offset, ch) in ('1'..='9').enumerate() {
+        assert_eq!(char_to_usage(ch), Some((0x1E + offset as u8, 0x00)));
+    }
+    assert_eq!(char_to_usage('0'), Some((0x27, 0x00)));
+
+    let cases = [
+        ('!', (0x1E, 0x02)),
+        ('@', (0x1F, 0x02)),
+        ('#', (0x20, 0x02)),
+        ('$', (0x21, 0x02)),
+        ('%', (0x22, 0x02)),
+        ('^', (0x23, 0x02)),
+        ('&', (0x24, 0x02)),
+        ('*', (0x25, 0x02)),
+        ('(', (0x26, 0x02)),
+        (')', (0x27, 0x02)),
+        ('-', (0x2D, 0x00)),
+        ('_', (0x2D, 0x02)),
+        ('=', (0x2E, 0x00)),
+        ('+', (0x2E, 0x02)),
+        ('[', (0x2F, 0x00)),
+        ('{', (0x2F, 0x02)),
+        (']', (0x30, 0x00)),
+        ('}', (0x30, 0x02)),
+        ('\\', (0x31, 0x00)),
+        ('|', (0x31, 0x02)),
+        (';', (0x33, 0x00)),
+        (':', (0x33, 0x02)),
+        ('\'', (0x34, 0x00)),
+        ('"', (0x34, 0x02)),
+        ('`', (0x35, 0x00)),
+        ('~', (0x35, 0x02)),
+        (',', (0x36, 0x00)),
+        ('<', (0x36, 0x02)),
+        ('.', (0x37, 0x00)),
+        ('>', (0x37, 0x02)),
+        ('/', (0x38, 0x00)),
+        ('?', (0x38, 0x02)),
+        (' ', (0x2C, 0x00)),
+        ('\n', (0x28, 0x00)),
+        ('\r', (0x28, 0x00)),
+        ('\t', (0x2B, 0x00)),
+    ];
+
+    for (ch, expected) in cases {
+        assert_eq!(
+            char_to_usage(ch),
+            Some(expected),
+            "unexpected mapping for {ch:?}"
+        );
+    }
+}
+
+#[test]
+fn char_to_usage_rejects_characters_outside_the_ascii_contract() {
+    for ch in ['é', '🙂', '\u{2603}'] {
+        assert_eq!(char_to_usage(ch), None, "unexpected support for {ch:?}");
+    }
+}