diff --git a/.trinity/seals/src_port::trios::crates::trios-chat::rings::CR-CHAT-04::src::padding_response_timing_fingerprint_guard.json b/.trinity/seals/src_port::trios::crates::trios-chat::rings::CR-CHAT-04::src::padding_response_timing_fingerprint_guard.json
new file mode 100644
index 0000000000..19e6a1dbe8
--- /dev/null
+++ b/.trinity/seals/src_port::trios::crates::trios-chat::rings::CR-CHAT-04::src::padding_response_timing_fingerprint_guard.json
@@ -0,0 +1,28 @@
+{
+  "built_by": "t27c-bootstrap@0.5.2+01d0a635f",
+  "closure": [],
+  "config": "gen=c,rust,verilog,zig;tests=zig",
+  "gen_hash_c": "sha256:8f61a351374d4a00c669c61f176b0b74c51f64fd93a316df6c8b490589cba95a",
+  "gen_hash_rust": "sha256:b864dbb042f38b3a78c8fe6243a593d51d287a16c1c9d70801f5dc048f9fc337",
+  "gen_hash_verilog": "sha256:f9e5656aad11599fea0ea8cb0f851e887f71b1ae27e832f65219e549a8816f62",
+  "gen_hash_zig": "sha256:24b90070ec9b4b213eb788eced8bf1b124cf88fae569eaa941c5aa953272055c",
+  "module": "port::trios::crates::trios-chat::rings::CR-CHAT-04::src::padding_response_timing_fingerprint_guard",
+  "ring": 12,
+  "seal_schema": 2,
+  "sealed_at": "2026-10-16T13:10:11Z",
+  "sealed_by": "t27c-bootstrap@0.5.2",
+  "spec_hash": "sha256:36bd058647fc50b62f90f5d45704656b55e70fb1e3e742ce2edb99239decc07f",
+  "spec_path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_response_timing_fingerprint_guard.t27",
+  "tests": {
+    "failed": 0,
+    "failing": [],
+    "forced": false,
+    "passed": 13,
+    "total": 13,
+    "vacuous": 0
+  },
+  "toolchain": {
+    "test_runner": "sha256:1982ae948e24d00c5d221ccec12dfce1eb01204b53e37b0f857f93b16d64629d",
+    "zig": "0.16.0"
+  }
+}
\ No newline at end of file
diff --git a/docs/reports/t27b_expectations.json b/docs/reports/t27b_expectations.json
index cfbb74965e..5086d83da8 100644
--- a/docs/reports/t27b_expectations.json
+++ b/docs/reports/t27b_expectations.json
@@ -900,6 +900,7 @@
   {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_length_class_transition_uniformity_guard.t27", "t27b": "pass"},
   {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_length_distribution_guard.t27", "t27b": "pass"},
   {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_oracle_timing_sidechannel.t27", "t27b": "pass"},
+  {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_response_timing_fingerprint_guard.t27", "t27b": "pass"},
   {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/safety_number.t27", "t27b": "pass"},
   {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-05/src/envelope_size_distribution_uniformity.t27", "t27b": "pass"},
   {"path": "specs/port/trios/crates/trios-chat/rings/CR-CHAT-07/src/blind_signature_sender_token.t27", "t27b": "pass"},
diff --git a/specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_response_timing_fingerprint_guard.t27 b/specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_response_timing_fingerprint_guard.t27
new file mode 100644
index 0000000000..9d1ca03e48
--- /dev/null
+++ b/specs/port/trios/crates/trios-chat/rings/CR-CHAT-04/src/padding_response_timing_fingerprint_guard.t27
@@ -0,0 +1,476 @@
+module port::trios::crates::trios-chat::rings::CR-CHAT-04::src::padding_response_timing_fingerprint_guard;
+
+// Port of gHashTag/trios crates/trios-chat/rings/CR-CHAT-04/src/padding_response_timing_fingerprint_guard.rs
+// (CR-CHAT-04 - Padding response timing fingerprint guard, Wave-143
+// Lane A, requirement R-CHAT-4).
+//
+// Padded and unpadded responses must cost the same time: an
+// observer timing the server reads off whether padding applied,
+// infers short from fast, and builds a binary classifier for the
+// message type. The rules, in the original's order: the batch
+// ceiling, the empty batch (accepted before the sample floor,
+// exactly as the original places it), the sample floor, then per
+// sample the zero-id probe and the repeated-id scan, then over
+// the whole batch the mean floor and the coefficient-of-
+// variation ceiling - the standard deviation over the mean,
+// scaled by a thousand and compared as the original's integer
+// cross-multiplication.
+//
+// The original returns Result<(), TimingFingerprintError>. This
+// port carries the verdict as a named struct (owner decision D5):
+// Ok first, then the six error variants in the original's
+// declaration order - HighCv, TooFew, LowMean, Duplicate,
+// ZeroId, TooMany - with every payload field: the measured and
+// ceiling CV (x1000) for HighCv, got and min for TooFew, the
+// got and min mean for LowMean, idx for the id rules, and got
+// and max for the batch ceiling.
+//
+// The original's u64::isqrt becomes a bisection over the whole
+// answer range - thirty-three halvings, exact for every u64, no
+// float anywhere. The BTreeSet dedup becomes a scan over the
+// samples already visited; the mean, variance and CV stay the
+// original's integer u64 arithmetic, the length widening through
+// the int cast.
+
+// Maximum CV numerator (x1000).
+pub const PRTF_MAX_CV_NUM: u64 = 200;
+
+// Maximum CV denominator (x1000).
+pub const PRTF_MAX_CV_DEN: u64 = 1000;
+
+// Minimum samples.
+pub const PRTF_MIN_SAMPLES: usize = 8;
+
+// Minimum mean timing in microseconds.
+pub const PRTF_MIN_MEAN_US: u64 = 50;
+
+// Maximum samples per batch.
+pub const PRTF_MAX_SAMPLES: usize = 512;
+
+// Sample ID length.
+pub const PRTF_SAMPLE_ID_LEN: usize = 16;
+
+// A timing sample record.
+pub struct TimingSample {
+    sample_id: [16]u8,
+    time_us: u64,
+}
+
+// Verdict codes: Ok(()) and TimingFingerprintError's variants, in declaration order.
+pub enum TimingFingerprintCode {
+    Ok,
+    HighCv,
+    TooFew,
+    LowMean,
+    Duplicate,
+    ZeroId,
+    TooMany,
+}
+
+// The verdict of the timing fingerprint validation, with every
+// error payload field.
+pub struct TimingFingerprintVerdict {
+    code: TimingFingerprintCode,
+    idx: usize,
+    got: usize,
+    bound: usize,
+    got64: u64,
+    bound64: u64,
+}
+
+// Whole-form equality over the fixed sixteen id bytes.
+pub fn ids16_equal(a: [16]u8, b: [16]u8) -> bool {
+    for i in 0..16 {
+        if (a[i] != b[i]) {
+            return false;
+        }
+    }
+    return true;
+}
+
+// The all-zero sample id - the original's [0u8; 16] probe.
+pub fn id16_zero(id: [16]u8) -> bool {
+    for i in 0..16 {
+        if (id[i] != 0) {
+            return false;
+        }
+    }
+    return true;
+}
+
+// Whether sample i repeats an earlier id - the original's
+// BTreeSet insert probe, answered by a scan.
+pub fn id_seen_before(samples: []const TimingSample, i: usize) -> bool {
+    for j in 0..i {
+        if (ids16_equal(samples[j].sample_id, samples[i].sample_id)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+// The integer square root of a u64 - the original's u64::isqrt,
+// answered by a bisection over the whole answer range. The
+// largest root of any u64 is 4294967295, and thirty-three
+// halvings settle the search exactly.
+pub fn isqrt64(v: u64) -> u64 {
+    var lo: u64 = 0;
+    var hi: u64 = 4294967295;
+    var mid: u64 = 0;
+    for _ in 0..33 {
+        if (lo <= hi) {
+            mid = (lo + hi) / 2;
+            if (mid * mid <= v) {
+                lo = mid + 1;
+            } else {
+                hi = mid - 1;
+            }
+        }
+    }
+    return hi;
+}
+
+// [VERIFIED] Validate padding response timing fingerprint.
+// Returns Ok only when every rule holds, checked in the
+// original's order: the batch ceiling, the empty batch (accepted),
+// the sample floor, then per sample the zero id and the repeated
+// id, then over the whole batch the mean floor and the CV
+// ceiling.
+pub fn validate_timing_fingerprint(samples: []const TimingSample) -> TimingFingerprintVerdict {
+    if (samples.len > PRTF_MAX_SAMPLES) {
+        return TimingFingerprintVerdict { code: TimingFingerprintCode.TooMany, idx: 0, got: samples.len, bound: PRTF_MAX_SAMPLES, got64: 0, bound64: 0, };
+    }
+    if (samples.len == 0) {
+        return TimingFingerprintVerdict { code: TimingFingerprintCode.Ok, idx: 0, got: 0, bound: 0, got64: 0, bound64: 0, };
+    }
+    if (samples.len < PRTF_MIN_SAMPLES) {
+        return TimingFingerprintVerdict { code: TimingFingerprintCode.TooFew, idx: 0, got: samples.len, bound: PRTF_MIN_SAMPLES, got64: 0, bound64: 0, };
+    }
+    for i in 0..samples.len {
+        if (id16_zero(samples[i].sample_id)) {
+            return TimingFingerprintVerdict { code: TimingFingerprintCode.ZeroId, idx: i, got: 0, bound: 0, got64: 0, bound64: 0, };
+        }
+        if (id_seen_before(samples, i)) {
+            return TimingFingerprintVerdict { code: TimingFingerprintCode.Duplicate, idx: i, got: 0, bound: 0, got64: 0, bound64: 0, };
+        }
+    }
+    const len64: u64 = @as(u64, samples.len);
+    var sum: u64 = 0;
+    for i in 0..samples.len {
+        sum = sum + samples[i].time_us;
+    }
+    const mean: u64 = sum / len64;
+    if (mean < PRTF_MIN_MEAN_US) {
+        return TimingFingerprintVerdict { code: TimingFingerprintCode.LowMean, idx: 0, got: 0, bound: 0, got64: mean, bound64: PRTF_MIN_MEAN_US, };
+    }
+    var var_sum: u64 = 0;
+    var diff: u64 = 0;
+    for i in 0..samples.len {
+        if (samples[i].time_us > mean) {
+            diff = samples[i].time_us - mean;
+        } else {
+            diff = mean - samples[i].time_us;
+        }
+        var_sum = var_sum + diff * diff;
+    }
+    const std_dev_x1000: u64 = isqrt64(var_sum / len64) * 1000;
+    var cv_x1000: u64 = 18446744073709551615;
+    if (mean > 0) {
+        cv_x1000 = std_dev_x1000 / mean;
+    }
+    const max_cv_x1000: u64 = PRTF_MAX_CV_NUM * 1000 / PRTF_MAX_CV_DEN;
+    if (cv_x1000 > max_cv_x1000) {
+        return TimingFingerprintVerdict { code: TimingFingerprintCode.HighCv, idx: 0, got: 0, bound: 0, got64: cv_x1000, bound64: max_cv_x1000, };
+    }
+    return TimingFingerprintVerdict { code: TimingFingerprintCode.Ok, idx: 0, got: 0, bound: 0, got64: 0, bound64: 0, };
+}
+
+// The sample ids of the fixtures, one byte repeated sixteen
+// times - the original's sid(byte) helper, entry by entry.
+pub const SID_01: [16]u8 = [16]u8{1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,};
+pub const SID_02: [16]u8 = [16]u8{2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,};
+pub const SID_03: [16]u8 = [16]u8{3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,};
+pub const SID_04: [16]u8 = [16]u8{4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,};
+pub const SID_05: [16]u8 = [16]u8{5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,};
+pub const SID_06: [16]u8 = [16]u8{6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,};
+pub const SID_07: [16]u8 = [16]u8{7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,};
+pub const SID_08: [16]u8 = [16]u8{8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,};
+pub const SID_09: [16]u8 = [16]u8{9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,};
+pub const SID_10: [16]u8 = [16]u8{10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,};
+pub const ZERO_ID16: [16]u8 = [16]u8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,};
+
+// The leading id bytes of the thirty-sample fixture.
+pub const PRTF_ID_BYTES_30: [30]u8 = [30]u8{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,};
+
+// The two id bytes of the too-many fixture: the original writes
+// the big-endian u64 of i + 1 into id[0..8], and for every value
+// in 1..=513 only the last two of those eight bytes can carry a
+// nonzero digit.
+pub const PRTF_ID6_513: [513]u8 = [513]u8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2,};
+pub const PRTF_ID7_513: [513]u8 = [513]u8{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 0, 1,};
+
+// **PRTF-01** - high CV rejected: seven samples at a hundred
+// microseconds and one at a hundred thousand - CV x1000 of 2624
+// over the ceiling of 200.
+test prtf_01_high_cv_rejected {
+    const samples: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 100, },
+        TimingSample { sample_id: SID_02, time_us: 100, },
+        TimingSample { sample_id: SID_03, time_us: 100, },
+        TimingSample { sample_id: SID_04, time_us: 100, },
+        TimingSample { sample_id: SID_05, time_us: 100, },
+        TimingSample { sample_id: SID_06, time_us: 100, },
+        TimingSample { sample_id: SID_07, time_us: 100, },
+        TimingSample { sample_id: SID_08, time_us: 100000, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.HighCv);
+    assert(v.got64 == 2624);
+    assert(v.bound64 == 200);
+}
+
+// **PRTF-02** - too few rejected: seven samples of a required
+// eight.
+test prtf_02_too_few_rejected {
+    const samples: [7]TimingSample = [7]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 1000, },
+        TimingSample { sample_id: SID_02, time_us: 1000, },
+        TimingSample { sample_id: SID_03, time_us: 1000, },
+        TimingSample { sample_id: SID_04, time_us: 1000, },
+        TimingSample { sample_id: SID_05, time_us: 1000, },
+        TimingSample { sample_id: SID_06, time_us: 1000, },
+        TimingSample { sample_id: SID_07, time_us: 1000, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.TooFew);
+    assert(v.got == 7);
+    assert(v.bound == 8);
+}
+
+// **PRTF-03** - low mean rejected: ten samples at ten
+// microseconds - a mean of ten under the floor of fifty.
+test prtf_03_low_mean_rejected {
+    const samples: [10]TimingSample = [10]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 10, },
+        TimingSample { sample_id: SID_02, time_us: 10, },
+        TimingSample { sample_id: SID_03, time_us: 10, },
+        TimingSample { sample_id: SID_04, time_us: 10, },
+        TimingSample { sample_id: SID_05, time_us: 10, },
+        TimingSample { sample_id: SID_06, time_us: 10, },
+        TimingSample { sample_id: SID_07, time_us: 10, },
+        TimingSample { sample_id: SID_08, time_us: 10, },
+        TimingSample { sample_id: SID_09, time_us: 10, },
+        TimingSample { sample_id: SID_10, time_us: 10, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.LowMean);
+    assert(v.got64 == 10);
+    assert(v.bound64 == 50);
+}
+
+// **PRTF-04** - duplicate rejected: the second sample repeats
+// the first's id.
+test prtf_04_duplicate_rejected {
+    const samples: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 1000, },
+        TimingSample { sample_id: SID_01, time_us: 1000, },
+        TimingSample { sample_id: SID_02, time_us: 1000, },
+        TimingSample { sample_id: SID_03, time_us: 1000, },
+        TimingSample { sample_id: SID_04, time_us: 1000, },
+        TimingSample { sample_id: SID_05, time_us: 1000, },
+        TimingSample { sample_id: SID_06, time_us: 1000, },
+        TimingSample { sample_id: SID_07, time_us: 1000, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.Duplicate);
+    assert(v.idx == 1);
+}
+
+// **PRTF-05** - zero id rejected under live timings.
+test prtf_05_zero_id_rejected {
+    const samples: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: ZERO_ID16, time_us: 1000, },
+        TimingSample { sample_id: SID_02, time_us: 1000, },
+        TimingSample { sample_id: SID_03, time_us: 1000, },
+        TimingSample { sample_id: SID_04, time_us: 1000, },
+        TimingSample { sample_id: SID_05, time_us: 1000, },
+        TimingSample { sample_id: SID_06, time_us: 1000, },
+        TimingSample { sample_id: SID_07, time_us: 1000, },
+        TimingSample { sample_id: SID_08, time_us: 1000, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.ZeroId);
+    assert(v.idx == 0);
+}
+
+// **PRTF-06** - too many rejected: 513 samples of a maximum
+// 512, built in a loop like the original's, each id carrying the
+// big-endian u64 of its index plus one. The batch rule fires
+// before any sample is examined.
+test prtf_06_too_many_rejected {
+    var samples: [513]TimingSample;
+    for i in 0..513 {
+        var id: [16]u8 = [16]u8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,};
+        id[6] = PRTF_ID6_513[i];
+        id[7] = PRTF_ID7_513[i];
+        samples[i] = TimingSample { sample_id: id, time_us: 1000, };
+    }
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.TooMany);
+    assert(v.got == 513);
+    assert(v.bound == 512);
+}
+
+// **PRTF-07** - the uniform batch accepted: ten samples stepping
+// by ten microseconds from a thousand - CV x1000 of 26.
+test prtf_07_valid_accepted {
+    const samples: [10]TimingSample = [10]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 1000, },
+        TimingSample { sample_id: SID_02, time_us: 1010, },
+        TimingSample { sample_id: SID_03, time_us: 1020, },
+        TimingSample { sample_id: SID_04, time_us: 1030, },
+        TimingSample { sample_id: SID_05, time_us: 1040, },
+        TimingSample { sample_id: SID_06, time_us: 1050, },
+        TimingSample { sample_id: SID_07, time_us: 1060, },
+        TimingSample { sample_id: SID_08, time_us: 1070, },
+        TimingSample { sample_id: SID_09, time_us: 1080, },
+        TimingSample { sample_id: SID_10, time_us: 1090, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.Ok);
+}
+
+// **PRTF-08** - an empty batch accepted, before the sample
+// floor, exactly as the original places it.
+test prtf_08_empty_accepted {
+    const samples: [0]TimingSample = [0]TimingSample{};
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.Ok);
+}
+
+// **PRTF-09** - the minimum-sample boundary accepted: eight
+// samples stepping by five from five hundred.
+test prtf_09_min_samples_accepted {
+    const samples: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 500, },
+        TimingSample { sample_id: SID_02, time_us: 505, },
+        TimingSample { sample_id: SID_03, time_us: 510, },
+        TimingSample { sample_id: SID_04, time_us: 515, },
+        TimingSample { sample_id: SID_05, time_us: 520, },
+        TimingSample { sample_id: SID_06, time_us: 525, },
+        TimingSample { sample_id: SID_07, time_us: 530, },
+        TimingSample { sample_id: SID_08, time_us: 535, },
+    };
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.Ok);
+}
+
+// **PRTF-10** - many uniform high values accepted: thirty samples
+// stepping by two from five thousand.
+test prtf_10_many_uniform_accepted {
+    var samples: [30]TimingSample;
+    var t: u64 = 5000;
+    for i in 0..30 {
+        var id: [16]u8 = [16]u8{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,};
+        id[0] = PRTF_ID_BYTES_30[i];
+        samples[i] = TimingSample { sample_id: id, time_us: t, };
+        t = t + 2;
+    }
+    const v = validate_timing_fingerprint(&samples);
+    assert(v.code == TimingFingerprintCode.Ok);
+}
+
+// The four helpers have direct tests (coverage: Untested 0).
+test ids16_helpers_answer {
+    assert(ids16_equal(SID_01, SID_01));
+    assert(!ids16_equal(SID_01, SID_02));
+    assert(id16_zero(ZERO_ID16));
+    assert(!id16_zero(SID_01));
+    const samples: [3]TimingSample = [3]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 1000, },
+        TimingSample { sample_id: SID_02, time_us: 1000, },
+        TimingSample { sample_id: SID_01, time_us: 1000, },
+    };
+    assert(!id_seen_before(&samples, 0));
+    assert(!id_seen_before(&samples, 1));
+    assert(id_seen_before(&samples, 2));
+}
+
+test isqrt64_answers {
+    assert(isqrt64(0) == 0);
+    assert(isqrt64(1) == 1);
+    assert(isqrt64(3) == 1);
+    assert(isqrt64(4) == 2);
+    assert(isqrt64(845) == 29);
+    assert(isqrt64(125) == 11);
+    assert(isqrt64(100) == 10);
+    assert(isqrt64(18446744073709551615) == 4294967295);
+}
+
+// Rule order is the original's: the batch ceiling before any
+// sample, the zero id before the duplicate, the duplicate before
+// the mean floor, the mean floor before the CV ceiling - and the
+// CV ceiling admitting its exact boundary.
+test rule_order_matches_original {
+    var flooded: [513]TimingSample;
+    for i in 0..513 {
+        flooded[i] = TimingSample { sample_id: ZERO_ID16, time_us: 1000, };
+    }
+    const v1 = validate_timing_fingerprint(&flooded);
+    assert(v1.code == TimingFingerprintCode.TooMany);
+
+    const twin_zeros: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: ZERO_ID16, time_us: 1000, },
+        TimingSample { sample_id: ZERO_ID16, time_us: 1000, },
+        TimingSample { sample_id: SID_02, time_us: 1000, },
+        TimingSample { sample_id: SID_03, time_us: 1000, },
+        TimingSample { sample_id: SID_04, time_us: 1000, },
+        TimingSample { sample_id: SID_05, time_us: 1000, },
+        TimingSample { sample_id: SID_06, time_us: 1000, },
+        TimingSample { sample_id: SID_07, time_us: 1000, },
+    };
+    const v2 = validate_timing_fingerprint(&twin_zeros);
+    assert(v2.code == TimingFingerprintCode.ZeroId);
+    assert(v2.idx == 0);
+
+    const dup_low_mean: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 10, },
+        TimingSample { sample_id: SID_01, time_us: 10, },
+        TimingSample { sample_id: SID_02, time_us: 10, },
+        TimingSample { sample_id: SID_03, time_us: 10, },
+        TimingSample { sample_id: SID_04, time_us: 10, },
+        TimingSample { sample_id: SID_05, time_us: 10, },
+        TimingSample { sample_id: SID_06, time_us: 10, },
+        TimingSample { sample_id: SID_07, time_us: 10, },
+    };
+    const v3 = validate_timing_fingerprint(&dup_low_mean);
+    assert(v3.code == TimingFingerprintCode.Duplicate);
+    assert(v3.idx == 1);
+
+    const low_mean_high_cv: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 0, },
+        TimingSample { sample_id: SID_02, time_us: 0, },
+        TimingSample { sample_id: SID_03, time_us: 0, },
+        TimingSample { sample_id: SID_04, time_us: 0, },
+        TimingSample { sample_id: SID_05, time_us: 0, },
+        TimingSample { sample_id: SID_06, time_us: 0, },
+        TimingSample { sample_id: SID_07, time_us: 0, },
+        TimingSample { sample_id: SID_08, time_us: 399, },
+    };
+    const v4 = validate_timing_fingerprint(&low_mean_high_cv);
+    assert(v4.code == TimingFingerprintCode.LowMean);
+    assert(v4.got64 == 49);
+
+    const boundary_cv: [8]TimingSample = [8]TimingSample{
+        TimingSample { sample_id: SID_01, time_us: 40, },
+        TimingSample { sample_id: SID_02, time_us: 40, },
+        TimingSample { sample_id: SID_03, time_us: 40, },
+        TimingSample { sample_id: SID_04, time_us: 40, },
+        TimingSample { sample_id: SID_05, time_us: 60, },
+        TimingSample { sample_id: SID_06, time_us: 60, },
+        TimingSample { sample_id: SID_07, time_us: 60, },
+        TimingSample { sample_id: SID_08, time_us: 60, },
+    };
+    const v5 = validate_timing_fingerprint(&boundary_cv);
+    assert(v5.code == TimingFingerprintCode.Ok);
+}