diff --git a/core/physics/atlas_packing.py b/core/physics/atlas_packing.py
new file mode 100644
index 00000000..867f3f46
--- /dev/null
+++ b/core/physics/atlas_packing.py
@@ -0,0 +1,108 @@
+"""core.physics.atlas_packing — Golden-Angle mode packing (ADR-0242).
+
+Construction-boundary lift of Poincaré polar coordinates into Cl(4,1) null
+points via :func:`algebra.cga.embed_point`. Runtime storage is pure 32-vectors
+only (no Poincaré attribute leaks).
+
+Separation uses the CGA null-point distance recovered from ``cga_inner``:
+
+    ⟨P,Q⟩ = −d²/2  ⇒  d = √(−2⟨P,Q⟩)
+
+which is the Euclidean distance of the embedded R³ points (see ``cga_inner``
+doc). This is the cohesion-plan ``d_min`` pin progressive form — not a full
+H² geodesic solver. Fail-closed if any pair has ``d < min_d``.
+
+Off-serve: do not import from ``chat/runtime.py`` (A-04 quarantine).
+"""
+
+from __future__ import annotations
+
+import math
+from typing import Sequence
+
+import numpy as np
+
+from algebra.cga import cga_inner, embed_point
+from core.physics.wave_manifold import WaveManifold
+
+PHI = (1.0 + math.sqrt(5.0)) / 2.0
+DEFAULT_MIN_D = 0.12
+
+
+class AtlasPackingError(ValueError):
+    """Fail-closed packing refusal (separation / bounds)."""
+
+
+def null_point_separation(p: np.ndarray, q: np.ndarray) -> float:
+    """CGA null-point separation d = √(max(0, −2⟨P,Q⟩))."""
+    inner = float(cga_inner(np.asarray(p, dtype=np.float64), np.asarray(q, dtype=np.float64)))
+    # Clamp tiny positive float dust from null-cone numerics.
+    return math.sqrt(max(0.0, -2.0 * min(0.0, inner)))
+
+
+def golden_angle_pack(
+    n: int,
+    alpha: float,
+    *,
+    min_d: float = DEFAULT_MIN_D,
+) -> list[np.ndarray]:
+    """Golden-Angle packing on the Cl(4,1) null cone (horosphere lift).
+
+    For k = 0..n-1:
+      θ_k = 2π k / φ
+      r_k = tanh(α √k)
+      (x,y) = (r cos θ, r sin θ) → embed_point → null 32-vector
+
+    Rejects with :class:`AtlasPackingError` if any pairwise separation < min_d.
+    """
+    if n < 1:
+        raise AtlasPackingError("n must be >= 1")
+    if not math.isfinite(alpha) or alpha <= 0.0:
+        raise AtlasPackingError("alpha must be a positive finite float")
+    if not math.isfinite(min_d) or min_d < 0.0:
+        raise AtlasPackingError("min_d must be a non-negative finite float")
+
+    modes: list[np.ndarray] = []
+    for k in range(n):
+        # 2π/φ ≈ 222.5°; packing-equivalent complement is the classic ~137.5° golden angle.
+        theta_k = 2.0 * math.pi * k / PHI
+        r_k = math.tanh(alpha * math.sqrt(float(k)))
+        x = r_k * math.cos(theta_k)
+        y = r_k * math.sin(theta_k)
+        mode = embed_point(np.asarray([x, y, 0.0], dtype=np.float64), dtype=np.float64)
+        modes.append(np.asarray(mode, dtype=np.float64))
+
+    for i in range(len(modes)):
+        for j in range(i + 1, len(modes)):
+            d = null_point_separation(modes[i], modes[j])
+            if d < min_d:
+                raise AtlasPackingError(
+                    f"Packing rejected: separation {d:.4f} between {i} and {j} "
+                    f"is less than required minimum {min_d:.4f}."
+                )
+    return modes
+
+
+def register_packed_modes(
+    modes: Sequence[np.ndarray],
+    manifold: WaveManifold,
+) -> tuple[int, ...]:
+    """Register packed null modes on a session WaveManifold. Returns indices.
+
+    Note: these are null-point modes for spectral span / packing geometry, not
+    unit-versor holographic seals (seal_mode would refuse non-closed versors).
+    """
+    indices: list[int] = []
+    for mode in modes:
+        indices.append(manifold.register_resonant_mode(mode))
+    return tuple(indices)
+
+
+__all__ = [
+    "PHI",
+    "DEFAULT_MIN_D",
+    "AtlasPackingError",
+    "null_point_separation",
+    "golden_angle_pack",
+    "register_packed_modes",
+]
diff --git a/core/physics/fibonacci_search.py b/core/physics/fibonacci_search.py
new file mode 100644
index 00000000..2d4b3df3
--- /dev/null
+++ b/core/physics/fibonacci_search.py
@@ -0,0 +1,174 @@
+"""core.physics.fibonacci_search — fixed-budget Fibonacci section search (ADR-0242).
+
+Deterministic 1D unimodal minimization for construction / calibration /
+GoldTether κ-style scalar brackets. Not a serve-path operator (A-04 quarantine).
+
+Fail-closed on:
+  * nonfinite objective values
+  * invalid bounds / budget
+  * sampled unimodality violation (values must decrease to the observed
+    minimum then increase when sorted by coordinate)
+"""
+
+from __future__ import annotations
+
+import math
+from dataclasses import dataclass, field
+from typing import Callable
+
+
+@dataclass(frozen=True, slots=True)
+class BoundedUnimodalObjective:
+    lower: float
+    upper: float
+    evaluation_budget: int
+    objective_id: str
+    objective_version: str
+
+    def __post_init__(self) -> None:
+        if self.evaluation_budget < 2:
+            raise ValueError("evaluation_budget must be >= 2")
+        if self.upper <= self.lower:
+            raise ValueError("upper bound must be strictly greater than lower bound")
+        if not math.isfinite(self.lower) or not math.isfinite(self.upper):
+            raise ValueError("bounds must be finite")
+
+
+@dataclass(slots=True)
+class SearchTrace:
+    best_observed_point: float
+    eval_sequence: list[float] = field(default_factory=list)
+    certificate: dict = field(default_factory=dict)
+
+
+def _fibonacci(n: int) -> int:
+    """F_0=0, F_1=1, … standard Fibonacci. n may be 0."""
+    if n < 0:
+        raise ValueError("fibonacci index must be non-negative")
+    a, b = 0, 1
+    for _ in range(n):
+        a, b = b, a + b
+    return a
+
+
+def _assert_sampled_unimodality(eval_values: dict[float, float]) -> None:
+    """Fail-closed if sorted samples are not unimodal about the observed min."""
+    sorted_points = sorted(eval_values.keys())
+    min_idx = 0
+    min_val = float("inf")
+    for i, x in enumerate(sorted_points):
+        v = eval_values[x]
+        if v < min_val:
+            min_val = v
+            min_idx = i
+
+    # Strictly non-increasing toward min (allow float ties).
+    for i in range(min_idx):
+        left = eval_values[sorted_points[i]]
+        right = eval_values[sorted_points[i + 1]]
+        if left < right - 1e-9:
+            raise ValueError(
+                "unimodality violation detected (multiple extrema): "
+                "values not decreasing before minimum."
+            )
+
+    # Strictly non-decreasing after min (allow float ties).
+    for i in range(min_idx, len(sorted_points) - 1):
+        left = eval_values[sorted_points[i]]
+        right = eval_values[sorted_points[i + 1]]
+        if left > right + 1e-9:
+            raise ValueError(
+                "unimodality violation detected (multiple extrema): "
+                "values not increasing after minimum."
+            )
+
+
+def fibonacci_section_search(
+    objective: BoundedUnimodalObjective,
+    func: Callable[[float], float],
+) -> SearchTrace:
+    """Fibonacci section search: exactly ``evaluation_budget`` function evals.
+
+    Returns :class:`SearchTrace` with ``best_observed_point``, ``eval_sequence``,
+    and a small certificate dict (budget, ids, bounds).
+    """
+    n = int(objective.evaluation_budget)
+    a = float(objective.lower)
+    b = float(objective.upper)
+
+    f_n_plus_1 = _fibonacci(n + 1)
+    f_n_minus_1 = _fibonacci(n - 1)
+    f_n = _fibonacci(n)
+
+    c = a + (f_n_minus_1 / f_n_plus_1) * (b - a)
+    d = a + (f_n / f_n_plus_1) * (b - a)
+
+    def _eval(x: float) -> float:
+        if x < objective.lower - 1e-12 or x > objective.upper + 1e-12:
+            raise ValueError(f"bounds violation: evaluated {x} outside [{objective.lower}, {objective.upper}]")
+        y = float(func(x))
+        if not math.isfinite(y):
+            raise ValueError(f"Objective function returned nonfinite value {y} at {x}")
+        return y
+
+    fc = _eval(c)
+    fd = _eval(d)
+    eval_sequence = [c, d]
+    eval_values: dict[float, float] = {c: fc, d: fd}
+
+    best_x = c if fc < fd else d
+    best_f = min(fc, fd)
+
+    k = 1
+    while k < n - 1:
+        if fc < fd:
+            b = d
+            d = c
+            fd = fc
+            f_n_minus_k_minus_1 = _fibonacci(n - k - 1)
+            f_n_minus_k_plus_1 = _fibonacci(n - k + 1)
+            c = a + (f_n_minus_k_minus_1 / f_n_minus_k_plus_1) * (b - a)
+            fc = _eval(c)
+            eval_sequence.append(c)
+            eval_values[c] = fc
+            if fc < best_f:
+                best_f = fc
+                best_x = c
+        else:
+            a = c
+            c = d
+            fc = fd
+            f_n_minus_k = _fibonacci(n - k)
+            f_n_minus_k_plus_1 = _fibonacci(n - k + 1)
+            d = a + (f_n_minus_k / f_n_minus_k_plus_1) * (b - a)
+            fd = _eval(d)
+            eval_sequence.append(d)
+            eval_values[d] = fd
+            if fd < best_f:
+                best_f = fd
+                best_x = d
+        k += 1
+
+    _assert_sampled_unimodality(eval_values)
+
+    certificate = {
+        "budget": objective.evaluation_budget,
+        "objective_id": objective.objective_id,
+        "objective_version": objective.objective_version,
+        "lower_bound": objective.lower,
+        "upper_bound": objective.upper,
+        "best_value": best_f,
+        "n_evals": len(eval_sequence),
+    }
+    return SearchTrace(
+        best_observed_point=float(best_x),
+        eval_sequence=list(eval_sequence),
+        certificate=certificate,
+    )
+
+
+__all__ = [
+    "BoundedUnimodalObjective",
+    "SearchTrace",
+    "fibonacci_section_search",
+]
diff --git a/docs/adr/ADR-0242-atlas-packing-and-fibonacci.md b/docs/adr/ADR-0242-atlas-packing-and-fibonacci.md
new file mode 100644
index 00000000..d75d0118
--- /dev/null
+++ b/docs/adr/ADR-0242-atlas-packing-and-fibonacci.md
@@ -0,0 +1,75 @@
+# ADR-0242: Hyperbolic Atlas Golden-Angle Packing and Fibonacci Search
+
+**Status**: Proposed — packing + Fibonacci search green on branch; acceptance path: Joshua review + merge  
+**Date**: 2026-07-14  
+**Deciders**: Joshua Shay + multi-model R&D (Gemini implementation pass)  
+**Traceability**: PR #37, parent ADR-0241 / cohesion master plan  
+**Related**: ADR-0003, ADR-0238, ADR-0241, `docs/analysis/core_cohesion_master_plan.md`, `docs/briefs/ADR-0242-atlas-packing-and-fibonacci-brief.md`  
+**Canonical path**: `docs/adr/`
+
+---
+
+## Context
+
+ADR-0241 established `WaveManifold` and `HolographicVaultStore`. Entity cohesion still needed:
+
+1. **Uniform resonant-mode packing** without resurrecting pointwise `core_ha` node IDs or Poincaré as runtime memory truth (ADR-0003).
+2. **Fixed-budget unimodal scalar search** for construction/calibration (e.g. GoldTether κ brackets) without scipy-as-truth or stochastic optimizers.
+
+## Decision
+
+### 1. Golden-Angle packing (`core/physics/atlas_packing.py`)
+
+For \(k = 0 \ldots n-1\):
+
+\[
+\theta_k = 2\pi k / \varphi,\qquad r_k = \tanh(\alpha\sqrt{k})
+\]
+
+Lift \((r\cos\theta, r\sin\theta, 0)\) via `algebra.cga.embed_point` to Cl(4,1) **null points**.
+
+**Separation pin:** CGA null-point distance from `cga_inner` contract \(\langle P,Q\rangle = -d^2/2\):
+
+\[
+d = \sqrt{-2\langle P,Q\rangle}
+\]
+
+Fail-closed (`AtlasPackingError`) if any pair has \(d < d_{\min}\) (default \(0.12\)).
+
+**Honest scope:** this \(d\) is the Euclidean distance of the embedded \(\mathbb{R}^3\) points (null-cone isometric readout), not a full hyperbolic \(H^2\) geodesic solver. Sufficient for the cohesion packing density gate.
+
+**No attribute leaks:** returned modes are pure `float64` 32-vectors. No stored θ/r.
+
+**Not holographic seals:** packed null points are session mode-registry geometry; `HolographicVaultStore.seal_mode` still requires closed unit versors.
+
+### 2. Fibonacci section search (`core/physics/fibonacci_search.py`)
+
+- `BoundedUnimodalObjective(lower, upper, evaluation_budget, objective_id, objective_version)`
+- `fibonacci_section_search(objective, func) -> SearchTrace`
+- Exactly `evaluation_budget` evaluations
+- Fail-closed on nonfinite, bounds violation, sampled unimodality violation
+- Certificate carries budget, ids, bounds, best value, n_evals
+
+### 3. Serve quarantine (A-04)
+
+Neither module may be imported from `chat/runtime.py`. Pinned in `tests/test_third_door_cohesion.py`.
+
+## Consequences
+
+### Benefits
+
+- Deterministic atlas packing for standing-wave mode placement
+- Algebra-native fixed-budget scalar search for κ / residual brackets
+- Continues `core_ha` deprecation (no node IDs / Poincaré runtime store)
+
+### Trade-offs
+
+- Separation is CGA null-point Euclidean distance, not full hyperbolic geodesic
+- Unimodality check is sample-based (only evaluated points), not a global oracle
+- Packing modes are null points, not unit versors — durable vault seal path remains separate
+
+## Validation
+
+- `tests/test_adr_0242_atlas_packing.py`
+- `tests/test_adr_0242_fibonacci.py`
+- `tests/test_third_door_cohesion.py` (serve quarantine + κ integration)
diff --git a/docs/research/third-door-blueprint-fidelity.md b/docs/research/third-door-blueprint-fidelity.md
index d0e027f8..261aa943 100644
--- a/docs/research/third-door-blueprint-fidelity.md
+++ b/docs/research/third-door-blueprint-fidelity.md
@@ -299,8 +299,8 @@ PY
 | Serve path not wired to wave / Fibonacci (containment) | 🟢 (AST-pinned in cohesion suite) |
 | Entity I-01…I-05 cohesion suite | 🟢 progressive pins in `test_third_door_cohesion.py` (I-02 float32-honest) |
 | Vault public `get_versor` ABI | 🟢 |
-| Golden-Angle atlas packing \(d_{\min}=0.12\) | 🔴 STOP → `docs/briefs/ADR-0242-atlas-packing-and-fibonacci-brief.md` |
-| Fibonacci κ search | 🔴 STOP → same brief |
+| Golden-Angle atlas packing \(d_{\min}=0.12\) | 🟢 ADR-0242 (`atlas_packing`; CGA null-point \(d\)) |
+| Fibonacci κ search | 🟢 ADR-0242 (`fibonacci_search`) |
 
 ### Subsumption map (Slice 2–3)
 | Operator | Delegation |
@@ -337,6 +337,6 @@ PY
 | `core_ha` deprecation — 🟢 no live tree + hygiene + Phase 0 grep | ADR-0241 / deprecation plan |
 | Durable holographic vault spectrum — 🟢 HolographicVaultStore | ADR-0241 |
 | Entity cohesion I-01…I-05 + Trace A/B | cohesion master plan |
-| Atlas packing + Fibonacci κ (ADR-0242) | cohesion master plan |
+| Atlas packing + Fibonacci κ (ADR-0242) — 🟢 packing + search | PR #37 / ADR-0242 |
 
 Closing a gap = flip its `xfail` in `tests/test_third_door_blueprint_fidelity.py` (or the ADR-0241 / cohesion suite) to a passing behavioral test and delete the matching characterization lock. That is the definition of "done right" here.
diff --git a/tests/test_adr_0242_atlas_packing.py b/tests/test_adr_0242_atlas_packing.py
new file mode 100644
index 00000000..a9e7b72d
--- /dev/null
+++ b/tests/test_adr_0242_atlas_packing.py
@@ -0,0 +1,73 @@
+"""ADR-0242 — Golden-Angle atlas packing behavioral pins."""
+
+from __future__ import annotations
+
+import math
+
+import numpy as np
+import pytest
+
+from algebra.cga import is_null
+from core.physics.atlas_packing import (
+    DEFAULT_MIN_D,
+    AtlasPackingError,
+    golden_angle_pack,
+    null_point_separation,
+    register_packed_modes,
+)
+from core.physics.wave_manifold import WaveManifold
+
+
+def test_golden_angle_pack_n_modes_min_geodesic_ge_0_12():
+    modes = golden_angle_pack(n=10, alpha=0.5)
+    assert len(modes) == 10
+    min_d = min(
+        null_point_separation(modes[i], modes[j])
+        for i in range(len(modes))
+        for j in range(i + 1, len(modes))
+    )
+    assert min_d >= DEFAULT_MIN_D
+
+
+def test_golden_angle_pack_rejects_when_alpha_too_dense():
+    with pytest.raises(AtlasPackingError, match="separation"):
+        golden_angle_pack(n=50, alpha=0.01)
+
+
+def test_packing_lift_produces_closed_or_null_legal_points():
+    modes = golden_angle_pack(n=5, alpha=0.3)
+    for m in modes:
+        assert is_null(m), "Lifted points must be legal null points in CGA"
+        assert m.shape == (32,)
+        assert m.dtype == np.float64
+
+
+def test_packing_deterministic_for_fixed_alpha_n():
+    modes1 = golden_angle_pack(n=20, alpha=0.4)
+    modes2 = golden_angle_pack(n=20, alpha=0.4)
+    for m1, m2 in zip(modes1, modes2):
+        np.testing.assert_allclose(m1, m2)
+
+
+def test_no_poincare_runtime_storage_in_wave_or_vault_metadata_truth():
+    manifold = WaveManifold()
+    modes = golden_angle_pack(n=5, alpha=0.3)
+    idxs = register_packed_modes(modes, manifold)
+    assert len(idxs) == 5
+    for m in manifold.resonant_modes:
+        assert m.shape == (32,)
+        assert m.dtype == np.float64
+        assert not hasattr(m, "theta")
+        assert not hasattr(m, "r")
+    # Modes are plain arrays — no Poincaré sidecar attributes.
+    assert not hasattr(modes[0], "theta")
+
+
+def test_null_point_separation_matches_euclidean_embed():
+    """cga_inner contract: ⟨P,Q⟩ = −d²/2 for embedded Euclidean points."""
+    from algebra.cga import embed_point
+
+    p = embed_point(np.asarray([0.1, 0.0, 0.0], dtype=np.float64), dtype=np.float64)
+    q = embed_point(np.asarray([0.4, 0.0, 0.0], dtype=np.float64), dtype=np.float64)
+    d = null_point_separation(p, q)
+    assert abs(d - 0.3) < 1e-9
diff --git a/tests/test_adr_0242_fibonacci.py b/tests/test_adr_0242_fibonacci.py
new file mode 100644
index 00000000..aad2182c
--- /dev/null
+++ b/tests/test_adr_0242_fibonacci.py
@@ -0,0 +1,77 @@
+"""ADR-0242 — Fibonacci section search behavioral pins."""
+
+from __future__ import annotations
+
+import pytest
+
+from core.physics.fibonacci_search import (
+    BoundedUnimodalObjective,
+    fibonacci_section_search,
+)
+
+
+def test_fibonacci_search_hits_known_unimodal_min_within_1e_3():
+    objective = BoundedUnimodalObjective(
+        lower=0.1,
+        upper=2.0,
+        evaluation_budget=20,
+        objective_id="test_id",
+        objective_version="v1",
+    )
+
+    def func(x: float) -> float:
+        return (x - 0.789) ** 2
+
+    trace = fibonacci_section_search(objective, func)
+    assert abs(trace.best_observed_point - 0.789) < 1e-3
+    assert len(trace.eval_sequence) == 20
+
+
+def test_fibonacci_search_eval_count_equals_budget():
+    objective = BoundedUnimodalObjective(
+        lower=-5.0,
+        upper=5.0,
+        evaluation_budget=15,
+        objective_id="test_id2",
+        objective_version="v1",
+    )
+
+    def func(x: float) -> float:
+        return x**2
+
+    trace = fibonacci_section_search(objective, func)
+    assert len(trace.eval_sequence) == 15
+    assert trace.certificate["n_evals"] == 15
+
+
+def test_fibonacci_search_rejects_nan_objective():
+    objective = BoundedUnimodalObjective(
+        lower=-1.0,
+        upper=1.0,
+        evaluation_budget=10,
+        objective_id="nan",
+        objective_version="v1",
+    )
+
+    def func(x: float) -> float:
+        return float("nan")
+
+    with pytest.raises(ValueError, match="nonfinite"):
+        fibonacci_section_search(objective, func)
+
+
+def test_fibonacci_search_unimodality_violation_fail_closed():
+    objective = BoundedUnimodalObjective(
+        lower=-2.0,
+        upper=2.0,
+        evaluation_budget=10,
+        objective_id="multi",
+        objective_version="v1",
+    )
+
+    def func(x: float) -> float:
+        # Multiple extrema: x^4 - x^2
+        return x**4 - x**2
+
+    with pytest.raises(ValueError, match="unimodality"):
+        fibonacci_section_search(objective, func)
diff --git a/tests/test_third_door_cohesion.py b/tests/test_third_door_cohesion.py
index 38083773..075c7aeb 100644
--- a/tests/test_third_door_cohesion.py
+++ b/tests/test_third_door_cohesion.py
@@ -269,11 +269,22 @@ def test_resonant_reconstruct_empty_refused():
 # --- ADR-0242 placeholder (Fibonacci not yet landed) --------------------------
 
 
-def test_fibonacci_search_module_absent_or_importable_placeholder():
-    """Until P5, fibonacci_search may be absent; if present it must not hit serve."""
-    spec = importlib.util.find_spec("core.physics.fibonacci_search")
-    if spec is None:
-        pytest.skip("ADR-0242 fibonacci_search not landed yet (expected until P5)")
-    # If present, ensure runtime still quarantined (A-04 already covers imports).
-    mod = importlib.import_module("core.physics.fibonacci_search")
-    assert hasattr(mod, "fibonacci_section_search")
+def test_fibonacci_search_goldtether_integration():
+    """Asserts Fibonacci search can optimize kappa and return a valid certificate."""
+    from core.physics.fibonacci_search import BoundedUnimodalObjective, fibonacci_section_search
+
+    objective = BoundedUnimodalObjective(
+        lower=0.1,
+        upper=2.0,
+        evaluation_budget=20,
+        objective_id="sha256_mock_id_for_goldtether_kappa",
+        objective_version="v1.0",
+    )
+
+    def synthetic_objective(kappa: float) -> float:
+        return (kappa - 0.789) ** 2  # unimodal minimum at 0.789
+
+    trace = fibonacci_section_search(objective, synthetic_objective)
+    assert abs(trace.best_observed_point - 0.789) < 1e-3
+    assert len(trace.eval_sequence) == 20
+    assert trace.certificate.get("budget") == 20