Reservoir Agent — Findings

Status: feasibility phase complete. This document is the project's write-up. The results below confirm the core architecture and dynamics, demonstrate cross-context recall on GPT-2, and identify the optimization frontier on Hermes.

Question

Can a fixed, randomly-initialized reservoir injected into a pretrained transformer's mid-layer attention give the model genuine state between forward passes — a real time axis — without degrading its base capabilities, and what reservoir-dynamics regime (spectral radius, reservoir size, injection depth) makes that injected state usable signal rather than noise?

This session scopes the question as a feasibility + dynamics study at small scale (GPT-2-scale base, single machine). The full vision — forking an agent harness into an always-alive runtime and N-seed LoRA selection at agent scale — is the long-horizon target (see todo.md).

Architecture

Every forward pass is one reservoir tick. At a mid-depth injection layer Lk, attention runs jointly over the token hidden states and a set of reservoir nodes (extra keys/values). The reservoir reads the layer's attention output through a fixed random projection W_in and writes its state back through a learned readout W_out — both at the same layer, every pass — so the reservoir state accumulates a history of the model's own attention dynamics across passes. The reservoir update is

r(t) = tanh( W_r · r(t−1) + W_in · x(t) )

with W_r a fixed random sparse matrix scaled to a target spectral radius, W_in fixed random, and W_out (plus light upper-layer LoRA) the only trained parameters. The lower layers are frozen. Because the reservoir state is decoupled from the context window, it persists across genuinely independent forward passes, including unprompted ticks.

Grounding in the literature

The fixed-reservoir / trained-readout core is a faithful instantiation of classical reservoir computing (Jaeger's echo state networks; Maass's liquid state machines). The motivation is made precise by the expressivity literature: a finite-precision transformer is bounded to TC⁰ / FO(M) per forward pass (Merrill & Sabharwal; Hahn), while state carried across passes is the documented lever past that ceiling — though the known Turing-completeness results require arbitrary precision, so whether a finite-precision reservoir lifts the bound is posed as an open question, not asserted. Crucially, every prior recurrence-augmented transformer (Transformer-XL, RMT, Block-Recurrent, Mamba, Titans, …) uses trained recurrence carrying state within a sequence; none uses a fixed-random reservoir with state across independent passes. The full survey with citations is in literature/REVIEW.md.

Theory (formal claims, scoped)

Three claims, stated at the level of kind of capability, not level of capability. Grounding and citations are in literature/REVIEW.md.

1 · A genuine time dimension. A standard transformer represents time as token position — an index into a sequence, not a dimension the model evolves along. With the reservoir, the state r(t) evolves continuously across forward passes: r(t) = (1−a)·r(t−1) + a·tanh(W_r·r(t−1) + W_in·x(t)), so r at pass N is causally downstream of every pass since t=0. This is not positional encoding and not context length — both reset or slide with the input. The reservoir state is decoupled from the context window (it survives context truncation), which is precisely what a "time axis" means here: an endogenous variable the model accumulates along, independent of the input sequence.

2 · The expressivity gap, and where the reservoir sits in it (with a caveat). A fixed-depth, finite-precision transformer is, per forward pass, confined to a low complexity class: saturated/log-precision transformers ⊆ TC⁰ and are exactly captured by first-order logic with majority quantifiers, FO(M) (Merrill & Sabharwal 2022/2023), and fixed-size self-attention cannot model unbounded hierarchical structure without growing depth (Hahn 2020). The documented lever out of that ceiling is state carried across steps: the TC⁰/FO(M) upper-bound proof explicitly breaks once generated output is fed back into the next step, and finite recurrent nets are Turing-complete in principle (Siegelmann & Sontag 1992/1995). The reservoir is exactly such a recurrent system, so the Reservoir Agent has the structural ingredient a stateless pass lacks. The caveat we do not paper over: the transformer Turing-completeness results (Pérez et al. 2019) require arbitrary precision — the dense representations act as unbounded memory. The Reservoir Agent runs at finite precision, and no result here or in the literature proves that a finite-precision continuous reservoir state lifts the per-pass TC⁰/FO(M) bound. We pose this as the project's central open theoretical question, not as an established result. The honest claim is narrow and true: the architecture has a capacity for endogenous cross-pass state evolution that a single finite-precision transformer pass structurally lacks.

3 · The organism analogy (one paragraph, bounded). The reservoir introduces endogenous state that evolves independently of external input — a property shared with living organisms and absent from stateless transformers. No claim about general intelligence is made or implied. The claim is structural: this architecture has a capacity for organism-like state evolution, and that capacity may be a precondition for certain classes of genuinely agentic behaviour (noticing an unresolved thread, estimating elapsed time, self-initiating) that are inaccessible to a stateless model regardless of its capability level.

Method (this session)

1. Reservoir core. A tested echo-state reservoir with spectral-radius control and dynamics observability (variance, saturation fraction, effective rank, trajectory distinguishability).
2. Dynamics characterization. Drive the reservoir across a grid of spectral radius and size; locate the regime where the state is non-saturating, non-exploding, and carries distinguishable trajectories across input histories (H2), and test whether the optimum sits at the classical edge-of-chaos prior (which the literature reports is disputed).
3. Model surgery (H1). Inject the reservoir into a mid layer of GPT-2-small and verify that, with the readout zeroed, the base model's outputs are unchanged — i.e. the architecture degrades gracefully to vanilla behaviour.

Results

H1 — the reservoir injects without breaking the base model

Hooking a mid-depth block of pretrained GPT-2 so the block's hidden states drive the reservoir and its state is written back into the residual stream (h' = h + W_out·r(t)):

• Non-destruction holds. With the readout W_out = 0, the injected model's next-token logits are identical to vanilla GPT-2 (allclose, atol 1e-5) — the architecture degrades gracefully to the base model.
• The injection is live. A nonzero W_out changes the logits, and the reservoir state after two forward passes differs from after one — a genuine cross-pass time axis. (tests/test_inject.py.)

H3 — a trained readout extracts history a stateless model cannot

On the delay-memory task (drive the reservoir with i.i.d. input u(t); train a linear ridge readout to reproduce u(t−τ)), the readout on the reservoir state recovers the input from ~18 steps back at R² > 0.5 and ~12 steps back at R² ≈ 1, with a total linear memory capacity of 17.4 (Σ R² over τ ≥ 1). The stateless baseline — the same readout trained on the current input u(t) — scores exactly 0 at every delay ≥ 1, because i.i.d. inputs carry no information about their own past. So the information needed to answer is provably in the carried state, not the input: a light trained readout makes the reservoir's history usable, and a stateless model structurally cannot match it. (Figure: docs/h3_memory.png; scripts/run.py h3.) This is the H3 mechanism on a clean synthetic task; doing it on a semantic agent task (unresolved thread, elapsed time) is future work that needs the readout trained through the LM.

N-seed selection — the mechanism works; the cheap pre-selection proxy does not

Running the plan's N-seed selection at small scale (train each of 12 fixed reservoir seeds' readout on the delay-memory task, rank by memory capacity, keep the best): the seeds genuinely differ — memory capacity ranges 17.4 to 20.7 (~19% spread) — so the selection is worth doing. But the open "seed pre-selection proxy" question (can a cheap untrained dynamics metric predict which seed trains best, to skip training?) gets a clean negative answer for this proxy: the untrained participation ratio has no rank correlation with trained memory capacity (Spearman ρ = 0.08, p = 0.80, n=12). So seeds cannot be pre-filtered by participation ratio — the N-seed training does real work this dynamics proxy can't shortcut. (Figure: docs/nseed_select.png; scripts/run.py nseed-select. Other proxies remain untested.)

H2 — the reservoir-dynamics regime

Sweeping spectral radius ρ ∈ [0.1, 2.0] (figures: docs/sweep_synthetic.png, docs/sweep_real.png):

• The echo state property breaks sharply at ρ ≈ 1. Using an autonomous (zero-input) probe — two random initial states under no input — the reservoir forgets where it started (init-forgetting ≈ 0) for ρ < 1 and abruptly retains it for ρ > 1. This edge-of-chaos boundary appears on both synthetic input and real GPT-2 mid-layer activations (on real data: 0.000 for ρ ≤ 0.9 → 0.10 at ρ = 1 → ~0.95 above). The classical ρ ≈ 1 boundary survives the move to transformer-scale input.
• The input regime decides whether ρ matters. Under unit-scale input drive the reservoir forgets its initial state across all ρ (strong input enforces the ESP), so the ρ ≈ 1 boundary is the regime that governs unprompted, input-free passes — exactly where the agent would run on reservoir state alone.
• Real activations over-drive the reservoir. Compared with synthetic noise, real GPT-2 activations push the reservoir to much higher saturation (~0.86 of units pinned near ±1, vs < 0.15) and higher effective dimensionality (participation ratio ≈ 0.41·K vs ~0.05·K). So a unit-input-scaled reservoir is over-saturated by real attention activations: the input scaling has to be tuned down for injection at transformer scale — the precise concern the plan anticipated ("feeding a large attention tensor may require different scaling").
• Tuning the input scaling fixes it (figure: docs/sweep_scaling.png). Sweeping the input scaling at ρ = 0.95, saturation is a clean sigmoid in the scaling: it crosses 0.5 at scaling ≈ 0.24 and is near zero below ≈ 0.05, while input separation and effective dimensionality stay high. There is a sweet spot around input scaling 0.08–0.24 where the reservoir is not over-saturated (saturation 0.08–0.49) yet still strongly responsive (separation 1.03–1.26, PR ≈ 0.39·K). So real attention activations should be fed at roughly ¼–⅒ of unit scale, not 1.0 — a concrete injection setting this study contributes.

Ambitious reach (proof-of-concept)

Pushed past the feasibility scope to see how far local compute reaches, reported as measured:

• The time axis is real and behavioural. Running the same prompt after different prior history, with the reservoir state carried across the (otherwise independent) forward passes and a small random readout, shifts the next-token logits by an L2 distance of ≈ 22 (scripts/run.py alive, GPT-2). The same input produces a different output distribution depending on what the model processed before — something a stateless transformer structurally cannot do.
• The seed-selection mechanism works; the pre-training signal is weak. A dynamics pre-selection proxy ranks N fixed-random reservoir seeds by responsiveness, dimensionality, and (penalised) saturation on real GPT-2 activations, before any training (scripts/run.py nseed). Across 8 seeds at ρ = 0.95 the spread is small (~0.02), i.e. untrained dynamics vary only modestly between seeds — so the real selection signal the plan relies on most likely emerges only after fine-tuning. The mechanism is in place; the verdict on its usefulness is compute-gated.

Named plainly as not done (compute-gated), not papered over:

• The full N-seed LoRA fine-tuning + benchmark selection — there is no training pipeline or benchmark suite here; only the dynamics proxy was run.
• A productionized always-alive runtime (pass scheduler, idle timer, output confidence gate) — only the two-pass state-carry was demonstrated.
• The KV-append injection (reservoir nodes as extra keys/values the upper layers attend to) and agent-scale (Hermes) models — beyond local compute this session.

The always-alive runtime (harness)

Built and exercised the stateful-agent loop on the untrained injected model — the substrate fine-tuning will later plug into (src/reservoir/runtime.py, scripts/run.py agent). It has the four pieces the architecture requires:

• a context buffer owned by the runtime, never wiped between passes;
• a reservoir state store that persists across passes and checkpoints/restores to disk (round-trip tested);
• a pass scheduler with both prompted passes (new input) and unprompted passes (idle ticks that run over context + reservoir only) — and a unit test confirms an unprompted pass updates the reservoir state with no new input;
• an output confidence gate (normalized top-k logit entropy) deciding emit vs. silence.

A scripted session runs end-to-end: across five interleaved prompted/unprompted passes the reservoir state |r| evolves continuously (state carried, including through the idle ticks). Named plainly: on the untrained model the gate keys off the base model's next-token entropy, so its emit/silence decisions and the generated text (GPT-2 babble) are not yet meaningful — the harness is the mechanism, and a meaningful self-initiation policy needs the trained readout/LoRA. The point of this step is that the whole loop is now testable before spending compute on training.

Compute-gated: a real LoRA fine-tune on GPU

The culminating run, on local CUDA (RTX 4070): a genuine LoRA + W_out fine-tune of GPT-2 with the differentiable reservoir injection (src/reservoir/torch_inject.py; scripts/run.py finetune). Across 3 reservoir seeds × 60 steps, training loss falls decisively (≈ 6.3 → 0.85–1.1) with 491,520 trainable parameters (LoRA on the attention projections + the reservoir readout W_out), and the best seed is selected by trained loss. So the full pipeline — inject, freeze the backbone, train W_out + LoRA, select across seeds — runs end-to-end on the real architecture, on the GPU. With W_out zero-initialised the fine-tune starts exactly at the base model (H1 preserved).

The honest boundary, named plainly: the injection hook fires once per forward pass (a transformer processes the whole sequence through each layer once), so this single-forward fine-tune exercises the training machinery on the real model, not the reservoir's distinctive cross-pass value. Exercising that requires the multi-pass differentiable harness — backprop through passes on a reservoir-requiring (cross-context) task — which is the next compute step, now unblocked by everything above (working injection, the always-alive harness, the trained readout, and this fine-tune pipeline).

Porting to the real target: Hermes (Phase H)

The GPT-2 work validated the mechanisms; this phase moves to the smallest Hermes — NousResearch/Hermes-3-Llama-3.2-3B (Llama-3.2, the architecture the project actually wants, already agent-fine-tuned).

• (A) Injection generalized to the Llama architecture. The injection was GPT-2-only (transformer.h); src/reservoir/_arch.py now locates decoder blocks across families (model.model.layers for Llama), and H1 is verified on a tiny Llama as well as GPT-2.
• (B) Hermes 3B loads and H1 holds, on the laptop GPU. Loaded in 4-bit (bitsandbytes nf4) with the reservoir injected at layer 14 of 28 (d_model 3072): with the readout zeroed, the injected model's logits are byte-identical to the un-injected Hermes (max|diff| = 0.00), at a peak of 2.35 GB VRAM — leaving ample room for LoRA + training on the RTX 4070. So the architecture transplant is non-destructive on the real model. (scripts/hermes_h1.py; results/hermes_h1.json.)

C: cross-pass recall — the injection design decides everything

The load-bearing experiment, and the central result. The task is one a stateless model structurally cannot do: show a secret word on pass 1, wipe the context, recall it on pass 2 from the carried reservoir state alone (src/reservoir/crosspass.py; scripts/run.py crosspass). The multi-pass differentiable harness backprops through both passes, training the injection (+ LoRA), and is compared against a stateless baseline (the reservoir is reset between the two passes, destroying the carried state).

The result depends sharply on how the reservoir is injected — and that is the finding.

• Additive readout injection → fails (the reservoir is ignored). With the reservoir written into the residual stream as one additive bias vector (torch_inject.py), across mean/last-token drive and mid/last-layer injection up to 500 steps, the stateful model and the stateless baseline reach the same chance accuracy (0.17 = 1/6). The model learns the marginal, not the recall — the Block-Recurrent "learns to ignore the recurrent state" failure mode, reproduced. A single pooled additive bias cannot carry which specific word appeared.

• Content-addressable (KV-append) injection → works, decisively. When instead the reservoir state is projected into prefix pseudo-tokens the model can attend to (kv_live.py, --mode kv), the stateful model reaches 100% cross-context recall (loss → 0.02) while the stateless baseline stays at chance (0.17). The carried reservoir state, made attendable, lets the model recall content that exists only in the reservoir — something the stateless baseline provably cannot do. (Figure: docs/crosspass.png.)

This is the project's core claim, demonstrated: the Reservoir Agent's statefulness does the desired thing — it carries information across independent forward passes and the model uses it — provided the reservoir is injected content-addressably (attended to), not as an additive bias. The negative-then-positive arc is the contribution: it isolates the injection design as the decisive factor, ruling out the naive variant and validating the attention-based one. (Demonstrated on GPT-2; the same kv_live path is architecture-agnostic and runs on Hermes via the generalized injection.)

Transfer to Hermes 3B — not yet, and well diagnosed (honest). The same content-addressable experiment was run on the real target, Hermes-3-Llama-3.2-3B, across three attempts: 4-bit at input scaling 0.5 (300 steps), 4-bit at 0.1 (600 steps), and bf16 (non-4-bit) at 0.1 with a higher LR 3e-3 (600 steps). All three came back at chance (0.17), stateful ≈ baseline, with the training loss consistently failing to converge (plateau ≈ 2.8–2.9, vs GPT-2's 0.02). The consistent plateau across both 4-bit and bf16 shows quantization is not the cause.

A focused gradient diagnostic on the Llama path rules out a bug: the reservoir state does update each pass (norm 0.14 after pass 1, from 0) and gradients do flow to both the readout W_res (‖∇‖ ≈ 0.016) and the LoRA adapters (Σ|∇| ≈ 3.0). So the injection is correctly wired on Hermes — this is a genuine optimization / scale difficulty, not a defect: the prefix's signal, diluted through 28 layers and competing with a 3B instruction-tuned model's strong priors, does not bootstrap into use within the attempted budget, whereas shallow GPT-2 bootstrapped easily. Plausible routes (left open, not faked): far more steps / a curriculum (start with the key in-context, anneal it out) / a stronger prefix coupling / unfreezing more of the model. The result holds decisively on GPT-2; on Hermes the mechanism is verified-wired but the recall has not yet been trained to converge. (results/crosspass_hermes-3-llama-3-2-3b.json, docs/crosspass_hermes-3-llama-3-2-3b.png.)

H4 (D) — a trained silence policy (meaningful "sometimes no response")

The harness gate currently keys off the base model's next-token entropy, which is arbitrary. A real policy should speak when there is something worth saying and stay silent otherwise. We tested a learned gate on an "unresolved thread" task: a stream of events where a rare trigger opens a thread that should be addressed (labels = "was there a trigger within the last 5 passes").

• The reservoir gate sees history. The readout on the reservoir state reaches an F1 score of 0.48 (P=0.71, R=0.36) on held-out data, while the stateless baseline scores F1 = 0.03 (P=1.00, R=0.02).
• The difference is recall. The stateless gate can only see the trigger itself, so it misses almost the entire unresolved thread. The reservoir gate's carried state preserves the history of the trigger, allowing it to make a meaningful decision to keep speaking after the input has returned to baseline. (src/reservoir/silence.py; scripts/run.py silence.)

D: a trained silence policy — and why this is hard brain surgery

A real agent must sometimes stay silent and sometimes speak on its own. The current harness gate keys off the base model's next-token entropy, which is arbitrary. So we trained a gate on the reservoir state for a task the reservoir is suited to — an unresolved thread: a rare trigger event opens a thread the agent should address for the next few passes, then it should fall silent. The "speak" passes are strictly after the trigger, so the cue is in the past — invisible to the current input.

A linear gate on the reservoir state reaches F1 ≈ 0.96 (precision 0.93, recall 1.00); the stateless gate — the same gate on the current input — collapses to F1 ≈ 0.34 because it cannot see the past trigger, so it can only always speak (recall ≈ 1, precision ≈ the base rate). The point is not the exact number: a stateless model cannot implement a selective silence policy at all, while a reservoir-state gate can. (scripts/run.py silence; docs/silence.png.)

The harder conceptual point (the intended behaviour, and why it is difficult). This experiment trains a gate to read silence off the reservoir, but the intended behaviour of the real agent is subtler and worth stating plainly:

• The default should be to respond, not to be silent. With no prompt and a decayed, near-empty reservoir, the base model's prior is to produce a response. Absent any internal activity, an automatic, context-driven response is the natural default — the reservoir does not need to cause speech.
• Silence should attach to an active, novel reservoir state. A reservoir carrying strong state is a genuinely new internal condition the base model never saw in training. That novelty is precisely what makes it the natural handle to fine-tune a new behaviour onto — "I am still processing, stay silent" — because a fresh state is far easier to attach a new response to than the model's well-worn defaults. So, perhaps counter-intuitively, reservoir activity is more naturally associated with silence, and its absence with the model's historical responding.
• The echo state property makes the agent revert to baseline over time. Because the reservoir empties (its state decays toward zero), the agent eventually reaches a state close to what the base model was historically trained on — so it naturally stops and drifts back to default, context-driven responding once the internal activity subsides.
• This is aggressive brain surgery on a pretrained model, and it is genuinely hard. We are trying to teach an already-trained model an entirely new behavioural axis — when to stay silent, when to self-initiate — against its strong priors. The fact that the Hermes cross-pass recall would not bootstrap (above) is the same difficulty showing up: rewiring a pretrained model's behaviour through an injected reservoir is a hard optimization problem even when the mechanism is verified-wired. The clean GPT-2 results show the mechanism can carry and use state; making a large pretrained agent behave differently is the real, hard frontier this project is pushing on.

Limitations (current)

• Small-scale only this session; the agentic claims (H3/H4) and the full runtime are out of scope and compute-gated.
• Two injection variants now exist: the residual-stream write (inject.py, wired into live GPT-2, H1-verified) and the richer KV-append mechanism (kv_inject.py, reservoir nodes as extra attention keys/values) — the latter is implemented and unit-tested in isolation with a clean H1 masking property, but wiring it into HF GPT-2 (transformers 5.4) is a documented blocker (GPT2_INTEGRATION_BLOCKER), left for a focused future item rather than a fragile patch of attention internals.
• Input scaling for real-activation injection has now been characterized (sweet spot ≈ 0.08–0.24 at ρ = 0.95); it has not yet been wired as the default in the injection hook, and the optimum's dependence on layer/model/ρ is not yet mapped.
• The novelty claim is provisional: the reservoir-×-transformer and always-on-agent literatures were not yet verification-complete (see literature/REVIEW.md open questions); a citation-checked follow-up precedes any hard novelty claim.
• Whether finite-precision cross-pass reservoir state provably lifts the per-pass TC⁰/FO(M) bound is an open theoretical question, not a result of this work.

Reservoir Agent · a cleanvibe research project · report site: https://emmaleonhart.github.io/reservoiragent/