hack-house/docs/stage-07-paper-draft.md

Consent-Gated Federated Onion Routing: Linkability and Anonymity-Set Effects of an In-Band Accept/Reject Relay Model

Draft — SS4 lead paper (G4 + RQ1 + RQ2). Results/Discussion filled from the frozen §6 pass.

Blinding status (prereg §2, binding). Sections 1–4, 7 were written blind while the confirmatory battery was still running. Sections 5–6 were filled once, after the full battery completed (180/180 cells) and the raw outputs were sealed (immutability anchor SHA256SUMS.txt), from the single frozen §6 inferential pass (docs/stage-06-analysis.md; results output/sor-confirmatory/20260720T060132Z/analysis/stage06-results.json). No number was inspected before that seal. The frozen prereg (sor-consent-prereg.md, SHA-256 f22331a72e0d0ccf38b787e63acabbe9d666456ec76076787a6d545c3193425b) is authoritative and unedited.

RQ2 posterior (ratified). The RQ2 dependent variable — a per-circuit adversary sender posterior — has a construction the frozen prereg left open; the construction (uniform mass over the observation-consistent anonymity set, grounded only in [Serjantov2002; Diaz2002]) was pre-specified blind and ratified by the operator before any RQ2 number was computed (docs/stage-05-rq2-posterior-clarification.md, RATIFIED). It is recomputable offline from the sealed per-circuit seeds.

Headline (honest null/negative). Neither hoped-for effect is confirmed. The bridge shows no measurable linkability leak (RQ1-P1 AUC below chance), and federation shrinks the anonymity set rather than growing it (RQ2-P1, a Holm-significant negative). We report this plainly — nulls and negatives are results.

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Abstract (skeleton — quantitative claims held until data + RQ2 ratification)

Onion-routing systems typically admit any relay that meets a directory's technical criteria; they do not model relay consent — a host's in-band, per-circuit choice to carry a given flow. We build and measure a consent-gated, federated, nested-SSH relay data plane in which every hop must explicitly accept or reject each circuit through a signed in-band handshake (Ed25519-authenticated, X25519 per-hop credentials), and in which relays are organized into houses that federate either through a shared bridge or through a directory. Treating this as a measurement instrument for a trust model's exposure (not a service that provides anonymity), we ask two confirmatory questions on a lab grid of two phones and a laptop: (RQ1) does a shared bridge introduce a measurable flow-linkability leak between a circuit's entry and exit segments, and does cover padding remove it; (RQ2) does federating relays across houses grow or shrink the anonymity set an adversary faces, and is any effect explained by bridge-concentration funnelling. All detectors are frozen and calibrated on known-linked/known-unlinked and equiprobable-sender fixtures before any confirmatory cell is run; all inference is bootstrap-based with BCa 95% CIs, Holm–Bonferroni-corrected across the confirmatory family. On a frozen 180-cell / 9,000-circuit battery, the calibration gate passes (known-linked AUC 1.00, known-unlinked 0.50) and neither hypothesis is confirmed: the bridge shows no measurable entry↔exit leak (RQ1-P1 AUC = 0.466, 95% CI [0.452, 0.480], below chance), so padding has nothing to suppress (RQ1-P2 ΔAUC = +0.011, CI [−0.002, +0.023], Holm-adjusted p = 0.46); and federation shrinks the anonymity set rather than growing it (RQ2-P1 ΔH = −0.96 bits, CI [−1.06, −0.86], Holm-significant), a genuine negative we report with equal prominence. The funnelling mechanism test (RQ2-P3) is degenerate as-instrumented and reported inconclusive. We frame these as honest null/negative findings for a specific lab consent-gate instrument, not general claims about consent-gated anonymity.

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1. Introduction

Anonymous-communication systems from onion routing [Reed1997; Dingledine2004] to its SSH-based descendant SOR [Egners2012] share a membership model that is essentially permissionless at the relay: a node participates if it meets directory or protocol criteria, and the routing layer does not represent whether a host consents to carry a particular circuit. Yet in social-trust and friend-to-friend designs — Freenet [Clarke2000], membership-concealing overlays [Vasserman2009], and social-graph routers such as Pisces [Mittal2012] and X-Vine [Mittal2012b] — who is willing to relay for whom is a first-class property. No existing system, to our knowledge, makes per-circuit relay consent an in-band, cryptographically-authenticated protocol step and then measures the privacy consequences of that gate. That gap — an accept/reject relay model whose linkability and anonymity-set behaviour are empirically characterised — is the novelty this work targets (G4).

We do not propose consent-gating as a deployed anonymity service. We build it as a defensive-measurement instrument: a controlled data plane whose knobs (bridge on/off, cover padding, federation topology) let us measure how a consent gate reshapes an adversary's view. Two consequences of the gate are non-obvious and testable:

1. A shared bridge is a linkability hazard (RQ1). When federated houses route through one shared bridge node, that node observes both the entry and exit segments of circuits crossing it. Modern flow-correlation attacks link such segments at high accuracy from timing/volume alone [NasrBH18; OhYMH22; RahmanSMGW20]. We ask whether our bridge exhibits a measurable entry↔exit correlation leak, and whether cover padding closes it.

2. Consent-gating can funnel, not just spread (RQ2). Federation intuitively enlarges the candidate-sender set and thus anonymity [Serjantov2002; Diaz2002]. But a consent gate means only willing relays carry traffic; if willingness concentrates on a few bridges, circuits funnel through them and the effective anonymity set may shrink. We therefore treat the sign of the federation effect as unknown a priori and report a shrink as prominently as a growth.

Contributions. (i) The design and instrument-grade implementation of a consent-gated, federated, nested-SSH relay data plane with signed in-band accept/reject and per-hop X25519 credentials (§3, §4). (ii) A pre-registered, frozen-detector confirmatory measurement of bridge linkability (RQ1) and the anonymity-set effect of federation (RQ2) on a lab grid (§4, §5). (iii) An honest, two-sided characterisation — including the funnelling mechanism test — of when consent-gated federation helps or harms anonymity. On this instrument the answer is a double null/negative: no bridge leak to close, and federation that measurably reduces the anonymity set — reported here without spin as the paper's evidentiary core.

Scope. Claims are deliberately restricted to the tested lab topology and scale (two phones + laptop, few houses); this is not an internet-scale or global-passive-adversary result (§7). The paired churn-resilience question (RQ3) and a QUIC/ssh3 transport arm [Michel2023] are pre-registered but held for a companion paper; this lead paper covers G4 + RQ1 + RQ2 only.

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2. Related work

Onion routing and SSH-based relays. Mixes and onion routing originate with Chaum [Chaum1981] and Reed–Syverson–Goldschlag [Reed1997], with Tor [Dingledine2004] as the dominant deployment. SOR [Egners2012] is the direct prior art: it layers onion routing over stock SSH tunnels, which is exactly our transport substrate. Nesting SSH inside SSH raises the well-known TCP-over-TCP throughput/latency pathology [Honda2005], motivating our latency-aware measurement and a (exploratory) QUIC-based ssh3 transport [Michel2023]; UDP-based latency work on onion services [AlAzad2023] is complementary. None of these model per-circuit relay consent, which is the axis we add and measure.

Flow correlation / linkability (RQ1). That an adversary seeing two segments of a flow can link them is established: low-cost traffic analysis [MurdochD05], realistic-adversary correlation on Tor [JohnsonWJSS13], and deep-learning correlators DeepCorr [NasrBH18] and DeepCoFFEA [OhYMH22] achieve high linking accuracy; packet-timing (Tik-Tok [RahmanSMGW20]) and deep fingerprinting [SirinamIJW18] show timing/volume suffice. We do not advance correlator state-of-the-art; we adopt a frozen, fixture-calibrated correlator (calibration gate §5) and use its AUC purely as an instrument reading of whether our bridge leaks — the contribution is the consent-gate/bridge measurement, not the attack.

Anonymity metrics and Sybil/directory concerns (RQ2). We quantify anonymity with the information-theoretic set metrics of Serjantov–Danezis [Serjantov2002] (entropy of the adversary posterior; effective set size S = 2^H) and Díaz et al. [Diaz2002] (normalized degree d = H/log₂N). Federation across mutually-distrusting houses evokes decentralised-directory and Sybil questions [Douceur2002; Winter2016] and statistical-disclosure exposure over repeated circuits [Danezis2003]. Our matched-N design isolates the topology effect (federated vs. single-house at equal total node count) rather than a node-count artifact.

Social-trust / consent-adjacent designs (G4 neighbours). The closest neighbours treat relaying willingness or social linkage as structural: Freenet's friend-to-friend mode [Clarke2000], membership-concealing overlays [Vasserman2009], Drac's social low-volume comms [Danezis2010], and social-graph routers Pisces [Mittal2012] / X-Vine [Mittal2012b] / STor [Zhou2011]. These encode trust in the graph; none makes consent an in-band, per-circuit, signed accept/reject protocol step whose linkability and anonymity-set consequences are then measured — the specific gap G4 fills.

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3. System design (the instrument)

The instrument is a nested-SSH relay data plane built into an existing zero-knowledge chat relay (hack-house), entirely within an isolated worktree. It has seven components (roadmap R1–R7); the subset load-bearing for this lead paper (RQ1 + RQ2, static selector, no model) is fully pinned by the freeze. Key mechanisms:

• Consent handshake (R5). Each hop receives a signed in-band consent request and must accept or reject before it will carry the circuit. Requests are Ed25519-signed by the originating persona and verified before acceptance; an unsigned or forged request is rejected. Per-hop credentials are X25519-sealed to the host's public key, so a hop credential decrypts only with that host's private key (no shared-symmetric secret).
• Nested-SSH circuits (R4). A circuit is a chain of SSH tunnels across grid hops; the entry and exit segments are the observable units for RQ1. Every hop's traffic is captured to an immutable per-hop pcap, written once and checksummed.
• Federation / bridge (R6). Relays are grouped into houses. Houses federate via a shared bridge node or via a directory; a circuit's federation path is chosen under split-knowledge topology constraints. The bridge is the shared observation point RQ1 probes and the concentration point RQ2's funnelling test probes.
• Determinism & provenance (R1–R3). All stochastic behaviour derives from a single --sor-seed; the seed, git SHA, and node-role→device mapping are echoed into an immutable manifest.json, and every relay event is appended to a SHA-256-sealed events.jsonl.
• Containment (binding). Every forwarder runs in an isolated engine only (assert engine != local or the run refuses). All traffic is self-generated to our own fixtures, lab-only. No external target, no live-network relay.

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4. Methods (pre-registered; frozen)

This study is a confirmatory factorial controlled comparison; the design, variables, seeds, detectors, and analysis were frozen and hashed on 2026-07-19 before any confirmatory cell ran.

4.1 Design matrix

Cells are organised per RQ with the other factors held at their declared control:

• RQ1 (linkability): bridge ∈ {off, on, on+padding} — 3 levels; topology held at single-house, selector static. (bridge-off+padding is declared N/A — padding is defined only for bridge-on.)
• RQ2 (anonymity set): topology ∈ {1-house-N, bridge-federated, directory-federated} at matched total node count N — 3 levels; bridge held off, selector static.

Full crossing is not run. Run order is randomised within each cell and the control arm is interleaved before and after treatments so grid calibration drift is caught. All stochastic elements are seed-controlled.

4.2 Dependent variables

• RQ1 — correlation AUC. Area under the ROC of the frozen flow-correlation detector scoring (entry-segment, exit-segment) pairs as same/different circuit, measured from the real per-hop pcaps. Unit of analysis: the (entry, exit) pair; 95% CI by bootstrap over circuit pairs.
• RQ2 — anonymity-set entropy H. Shannon entropy of the adversary's posterior over candidate senders per circuit; effective set size S = 2^H [Serjantov2002], normalized d = H/log₂N [Diaz2002]; Miller–Madow finite-sample bias correction; 95% CI by bootstrap over circuits. Unit of analysis: the circuit. ΔH = H(federated) − H(single-house, matched N).

  Construction (ratified). The prereg pins this DV as a per-circuit posterior but does not give the posterior construction rule. The construction — uniform mass over the observation-consistent anonymity set A_i (the circuits sharing an exit signature within a run), grounded only in [Serjantov2002; Diaz2002] — was pre-specified blind and ratified in docs/stage-05-rq2-posterior-clarification.md. It is recomputed offline from the sealed per-circuit seeds (deterministic circuit assembly), so no RQ2 number depended on inspecting the battery before it sealed.

4.3 Sampling & power

R = 30 independent seeded runs per cell; each run builds C = 50 circuits (≥ 1500 scored pairs per cell for RQ1). The target is precision, not a formal power analysis: ≥ 1500 pairs yields an expected bootstrap 95% CI half-width on AUC ≤ 0.03, enough to resolve the RQ1 floor away from 0.5. One base seed S0 = 20260719; per-cell seed = SHA256(S0 ‖ cell_id ‖ run_index) truncated to u64, echoed into every manifest. Stopping rule: all cells × R runs run to completion — no optional stopping, no interim looks; an uninformative cell is reported inconclusive, never extended to chase significance.

Apparatus (disclosed). All relay hops ran as isolated Docker containers on a single engine host (the laptop; grid/device-map.json, isolated_engine_host_count = 1, Docker 27.5.1). The two phones were consenting endpoints, not forwarders. Node distinctness is thus container-level (≥ 3 distinct containers per circuit), and matched-N is pinned from the containerised node count per manifest; cross-machine effects are out of scope (§7).

4.4 Frozen detectors and the instrument-validation gate

Detectors (correlator, entropy estimator, classifier) are written and calibrated only on the instrument-validation fixtures — known-linked/known-unlinked control pairs and equiprobable-sender synthetic sets — before any confirmatory cell is run; no per-cell tuning is permitted. The battery ran only after all six boolean gate items passed green: (1) 3-hop end-to-end delivery with per-hop pcap + checksum; (2) seeded reproducibility (same seed → identical circuit-build sequence); (3) correlator calibration (known-linked AUC ≈ 1, known-unlinked ≈ 0.5); (4) entropy calibration (H = log₂N for N equiprobable senders); (5) isolation (assert engine != local or refuse); (6) provenance integrity (replayed fixture → schema-valid events.jsonl whose SHA-256 matches the manifest; append-only).

4.5 Analysis plan

Effect size + 95% CI for every comparison; p-values never reported alone. All inference is bootstrap/permutation-based (10,000 resamples, BCa intervals; 3-seed spot-check to MC error).

• RQ1-P1 (leak). Bridge-on correlation AUC, bootstrap 95% CI. Confirmation gate = CI excludes 0.5 (leak present); null if CI includes 0.5. Materiality is a separate label: CI lower bound ≥ 0.60 ⇒ "material leak"; between 0.5 and 0.60 ⇒ "weak-but-real leak."
• RQ1-P2 (padding efficacy). ΔAUC = AUC(bridge-on, no-pad) − AUC(bridge-on, +pad); paired bootstrap 95% CI. Padding effective iff ΔAUC CI > 0.
• RQ2-P1 (federation effect, two-sided). ΔH bootstrap 95% CI; the sign is not presumed. grow if CI > 0; honest shrink (reported with equal prominence) if CI < 0; inconclusive if it spans 0.
• RQ2-P3 (funnelling mechanism). Spearman ρ between top-k=3 bridge concentration and per-circuit H, 95% CI; negative ρ quantifies funnelling.
• Multiple comparisons. Holm–Bonferroni over the frozen family of 7 confirmatory tests {RQ1-P1, RQ1-P2, RQ2-P1, RQ2-P3, RQ3-P1-perf, RQ3-P1-latency, RQ3-P2}; the 4 lead-paper tests are reported at Holm-adjusted multipliers 7, 6, 5, 4 (conservative embedding — see docs/stage-05-holm-clarification.md, ratified). EXPLORATORY results (QUIC transport; any post-hoc contrast) are labelled and excluded from the confirmatory column.
• Data exclusion (pre-data). A run is quarantined (logged, never silently dropped) only on a data-integrity failure (SHA mismatch, pcap checksum failure, in-place edit, or non-reproducing seed). No performance-based exclusions.
• Bootstrap implementation (method-faithful, not method-substituted). The frozen BCa bootstrap does an O(n) leave-one-out jackknife whose per-fold statistic is the O(pos×neg) AUC double loop — structurally intractable at the RQ1 scale (n = 75,000 pooled pairs; the RQ1-P2 ΔAUC evaluates AUC twice per resample). RQ1-P1 and RQ1-P2 CIs are therefore computed by a performance-faithful bootstrap that reproduces the frozen stats.bootstrap_ci bit-for-bit (identical random.Random(seed) resample sequence, a vectorised AUC proven equal to the frozen detector including the average-rank tie path, and the frozen BCa endpoints/jackknife); a committed --verify self-check asserts point/lo/hi/method agree to 1e-12. RQ2-P1 and RQ2-P3 remain on the unmodified frozen paths. No point estimate, CI gate, or decision is changed.

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5. Results

All numbers below come from the single frozen §6 pass on the sealed 180-cell battery and are deterministically regenerable (docs/stage-06-analysis.md; seed S0 = 20260719; 10,000 BCa resamples; α = 0.05). Every reported decision is a pre-registered CI gate; p-values order only the Holm step-down.

5.1 Instrument-validation gate report

The battery ran only after all six boolean gate items passed; the confirmatory-relevant calibration, recomputed independently on the §5 synthetic fixtures (40 seeds), holds: known-linked mean AUC = 1.0000 (criterion ≥ 0.95) and known-unlinked mean AUC = 0.5036 (criterion 0.40–0.60). Entropy calibration returns H = log₂N on equiprobable synthetic senders. Because the correlator is calibrated on fixtures and never fit to confirmatory-cell data, the measured AUCs below are reportable as instrument readings; had calibration failed, no AUC would be reported.

5.2 RQ1 — bridge linkability

RQ1-P1 (leak). On the bridge-on / no-pad arm the pooled (entry, exit) pair set (n = 75,000 pairs; 1,500 linked / 73,500 unlinked) yields AUC = 0.4660, BCa 95% CI [0.4523, 0.4798]. The CI excludes 0.5 but lies below it, so the frozen gate returns anomaly-below-chance, not leak. The correlator does not link entry↔exit segments better than chance on the bridge-on traffic; it sits marginally below chance — an unexplained artifact of the pooled correlator on this as-instrumented traffic (this is the no-pad arm, so no cover stream is involved), not a linkability finding — so we report no measurable leak. The two-sided rejection at AUC = 0.5 is in the wrong direction and is not evidence of linkability.

RQ1-P2 (padding efficacy). Pairing the bridge-on / no-pad and bridge-on / +padding arms by shared run index (n = 30 paired runs) gives paired ΔAUC = +0.0113, BCa 95% CI [−0.0025, +0.0234] (per-run ΔAUCᵢ range ≈ [−0.080, +0.081], straddling zero). The CI spans 0 → frozen gate padding-ineffective (raw p = 0.091). No significant padding effect on measured linkability; this is moot given RQ1-P1 found no leak to suppress, and is reported because the frozen test specifies it.

5.3 RQ2 — anonymity-set effect of federation

RQ2-P1 (federation effect, two-sided). Over the ratified per-circuit posterior (Miller–Madow H on the observation-consistent anonymity set), the federated arm (pooled bridge-federated + directory-federated, 3,000 circuits) versus matched-N single-house (1,500 circuits) gives ΔH = −0.9587 bits, BCa 95% CI [−1.0559, −0.8641]. The CI is strictly below 0 → frozen gate shrink. Federation, as instrumented, reduces the per-circuit anonymity set by ≈ 0.96 bits relative to a matched-N single house — the opposite of RQ2's motivating hypothesis. Per the two-sided pre-registration this negative is reported with equal prominence; we do not re-frame it as federation "helping."

RQ2-P3 (funnelling mechanism). Spearman ρ between top-k = 3 willing-bridge concentration and per-circuit H (bridge-federated arm, n = 1,500) is ρ = 0.0000, CI [0.0000, 0.0000] (percentile fallback) → inconclusive. The concentration series has no variance: the bridge-federated topology assigns a fresh willing bridge per circuit seed, so willing-bridge reuse is minimal and the top-3 concentration is effectively constant. Spearman is undefined on a zero-variance covariate. This is the as-instrumented degeneracy flagged in advance (§7; the stage-05 RQ2 instrument caveat), not a null of a well-posed mechanism test — the funnelling mechanism is not testable on this instrument as built.

5.4 Holm-corrected confirmatory summary

Holm–Bonferroni over the frozen family of 7 (reporting the 4 lead-paper tests at conservative multipliers 7, 6, 5, 4, ordered by ascending raw p):

Test	Effect	Point	95% CI (BCa)	Frozen decision	raw p	Holm adj-p (m=7)	Reject @ .05
RQ1-P1	AUC (bridge-on)	0.4660	[0.4523, 0.4798]	anomaly-below-chance	0.000	0.000	yes*
RQ2-P1	ΔH (fed − single)	−0.9587 bits	[−1.0559, −0.8641]	shrink	0.000	0.000	yes
RQ1-P2	ΔAUC (nopad − pad)	+0.0113	[−0.0025, +0.0234]	padding-ineffective	0.091	0.456	no
RQ2-P3	Spearman ρ	0.0000	[0.0000, 0.0000]	inconclusive	1.000	1.000	no

* RQ1-P1 rejects H0: AUC = 0.5 in the wrong direction (below chance) and is therefore not evidence of a leak. Two tests survive Holm at α = 0.05: RQ1-P1 (anomaly-below-chance) and RQ2-P1 (shrink — a negative effect). One exploratory contrast (labelled, excluded from the Holm family): the bridge-federated-only ΔH = −3.63 bits with a degenerate CI (near-single-member posterior, mᵢ ≈ 1), reported only for transparency and consistent with the RQ2-P3 degeneracy.

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6. Discussion

A double null/negative, reported without spin. The two motivating hypotheses of the consent gate — that a shared bridge leaks entry↔exit linkability (RQ1) and that federation grows the anonymity set (RQ2) — are both unsupported on this instrument, and the one Holm-significant directional effect points against the design's motivation.

RQ1 — no bridge leak to close. The frozen, fixture-calibrated correlator (linked AUC 1.00, unlinked 0.50) reads the bridge-on traffic at AUC 0.466 — statistically distinguishable from chance but below it, which the pre-registered gate correctly refuses to call a leak. We do not have a substantiated mechanism for the slight below-chance offset; it is a small artifact of the pooled correlator on this as-instrumented traffic (and it is not a padding effect — this is the no-pad arm, which carries no cover stream). Because there is no measurable leak, padding efficacy (RQ1-P2) is moot: ΔAUC is indistinguishable from zero, exactly as expected when there is nothing to suppress. The honest reading is that at this lab scale and topology, the shared bridge is not a measurable flow-linkability hazard for our frozen correlator — a scoped negative, not a claim that shared bridges are safe against a state-of-the-art adversary (§7).

RQ2 — federation shrinks the anonymity set. The evidentiary core is the Holm-significant ΔH = −0.96 bits: under the ratified adversary posterior, federating across houses reduces the effective candidate-sender set relative to a matched-N single house. This is the funnelling outcome anticipated as a live possibility in the introduction — a consent gate carries traffic only over willing relays, and when willingness concentrates, circuits funnel and anonymity contracts. The pre-registration framed RQ2-P1 two-sided precisely so this result is reported "with equal prominence"; it is a genuine negative finding about consent-gated federation, not a failure to detect an effect. We deliberately do not re-slice cells or hunt subgroups to recover a "federation helps" story.

Why the funnelling mechanism test is inconclusive. RQ2-P3 would have connected the ΔH shrinkage to bridge concentration directly, but the instrument as built assigns a fresh willing bridge per circuit seed, so the top-3 concentration covariate has no variance and Spearman is undefined. The mechanism is therefore not testable on this instrument — an honest limitation carried into §7, not evidence against funnelling. The exploratory bridge-federated-only ΔH = −3.63 bits (near-single-member posterior) is consistent with a funnelling reading but carries no confirmatory weight.

Takeaway. For this specific consent-gated, federated, nested-SSH instrument at lab scale, the consent gate's measured privacy consequences are (i) no bridge linkability leak and (ii) a reduction in the federation anonymity set. Both are scoped, honest results; neither generalises to internet scale or to a stronger adversary (§7). The value of the study is the pre-registered, frozen-detector method that let a hoped-for effect fail cleanly and a negative effect surface without being explained away.

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7. Limitations & threats to validity

• Scale / adversary model (External). The grid is two phones + a laptop and few houses; this is not internet-scale and not a global passive adversary. Claims are scoped to the tested topology/scale; entropy CIs are wide at small node counts (accepted, node counts reported).
• Node distribution (External, disclosed). All relay hops executed as isolated Docker containers on a single engine host (the laptop; isolated_engine_host_count = 1, recorded in grid/device-map.json). The two phones were consenting endpoints, not forwarders — they cannot host an isolated engine. Node distinctness for RQ1/RQ2 is therefore container-level (≥ 3 distinct containers per circuit), not physical-machine-level; matched-N is pinned from the containerised node count per manifest. This satisfies the containment law (every forwarder runs in an isolated engine, engine ≠ local) but means cross-machine timing effects are out of scope; physical multi-host distribution is named future work.
• Construct. Self-generated fixture traffic is not real user traffic (inherent to lab measurement; fixtures versioned/checksummed). A single correlator's AUC stands in for "linkability" and plug-in H for "anonymity" — mitigated by fixture calibration (§4.4) and by reporting S = 2^H and normalized d; a second entropy estimator (NSB) is reported EXPLORATORY as a sensitivity check.
• Internal. Thermal/background load and device heterogeneity are mitigated by randomised order, interleaved controls, per-session idle baselines, and a pinned node-role→device mapping. Detector-tuning contamination is eliminated by pre-battery freezing on fixtures.
• RQ2 construction dependency. The RQ2 result depends on the ratified posterior construction (§4.2); the construction is pre-specified blind, two-sided, and grounded only in cited metrics — but it is a specification the frozen prereg did not pin, and the ΔH = −0.96 bits finding should be read as conditional on it.
• Funnelling mechanism not testable as-instrumented (RQ2-P3). The bridge-federated topology assigns a fresh willing bridge per circuit seed, so the top-3 concentration covariate has zero variance and the Spearman mechanism test is degenerate (ρ = 0, inconclusive). This was flagged in advance; it means the mechanism behind the RQ2-P1 shrinkage is not empirically resolved on this instrument, only its magnitude. A topology with realistic willing-bridge reuse would be needed to test funnelling directly.
• Dual-use (ethics). An onion-routing data plane is dual-use; the defensive-measurement framing and containment envelope are load-bearing and binding, and the framing is red-teamed at stage 08.

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8. Deviations from pre-registration

Tracked only in stage-05 sor-consent-deviations.md (none edit the frozen prereg). Three clarifications recorded: the Holm family-size restatement (docs/stage-05-holm-clarification.md, ratified), the RQ2 posterior construction (docs/stage-05-rq2-posterior-clarification.md, ratified), and the RQ1-P2 run-index pairing (docs/stage-05-rq1p2-pairing-clarification.md, freeze-derived / ratified). One implementation note carried in §4.5: the RQ1 CIs use a performance-faithful bootstrap proven bit-for-bit equal to the frozen stats.bootstrap_ci (committed --verify), so no point estimate, CI gate, or decision is substituted. The frozen prereg SHA is unchanged (f22331a72e…).

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(Full bibliography: ~/coding/sci-method/stages/01-literature/output/sor-consent-bibliography.md. Integrity flags carried forward: [Stutzbach2006] secondary-sourced; [Constantinides2026] recent preprint — neither is load-bearing in this lead paper.)