diff --git a/decisions/architecture.md b/decisions/architecture.md
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@@ -598,4 +598,28 @@ Technical foundation decisions that constrain implementation: engine, client-ser
 
 ---
 
+### D-169: Implant UI component library — Control node tree with custom Theme
+- **Date:** 2026-04-05
+- **Decision:** The implant UI (all diegetic neural overlay panels — star map info, travel planner, station profiles, GTTR reader, cargo manifest, etc.) uses **Godot Control node components** composed in scenes, styled via a shared `Theme` resource. Not `_draw()` draw-objects, not hand-rolled rendering.
+- **Rationale:** The implant system is tagged as dynamic — different hardware, upgrades, damage states, and faction overlays will change the UI's look and behavior at runtime. This requires layout automation (reflow, resize, expand/collapse), accessibility support, and theme swapping — all things Godot's Control tree provides and a `_draw()` approach would need to reimplement. The team (Tyre, Stig, Araminta) initially favored `_draw()` for pixel control, but the dynamic implant requirement makes Control nodes the better long-term investment.
+- **Architecture:**
+  - `ImplantPanel` — `PanelContainer` with theme override, serves as root for any implant overlay
+  - `ImplantHeader` — `HBoxContainer` (title label + subtitle label)
+  - `ImplantSeparator` — `HSeparator` with theme override
+  - `ImplantDataRow` — `HBoxContainer` (key label + value label, two-column)
+  - `ImplantTextBlock` — `RichTextLabel` for wrapping narrative text
+  - `ImplantStatusBadge` — colored dot + label
+  - `ImplantProgressBar` — two-tone, no gradients
+  - `ImplantTabRow` — uppercase labels, underline-active pattern
+  - `ImplantExpandable` — chevron + collapsible section
+  - Theme resource (`.tres`) defines: colors (primary, dim, accent active/positive/negative/warning), spacing (line height, separator padding, panel padding), font sizes (header, body, small, caption)
+  - Different implant hardware swaps the entire Theme resource at runtime
+- **Rejected alternative:** R-NNN `_draw()` RefCounted components — pixel-precise, zero scene tree overhead, but would require reimplementing layout automation, scroll, and interaction handling as the implant system grows. Correct for a static HUD; wrong for a dynamic system.
+- **Raised by:** Jeroen + Tyre/Stig/Araminta design discussion, 2026-04-05
+- **Dissent:** Tyre and Stig initially favored `_draw()` for aesthetic control. Reversed when the dynamic implant requirement was surfaced.
+- **Semantic color roles:** `PRIMARY_TEXT` (#c8d0e0), `DIM_TEXT` (#667788), `ACCENT_ACTIVE` (#f0d060), `ACCENT_POSITIVE` (#44aa66), `ACCENT_NEGATIVE` (#aa4444), `ACCENT_WARNING` (#aa8844), `SEPARATOR` (#c8d0e0 at 12%)
+- **Interaction pattern:** Invisible until touched. Hover shows 0.3 alpha rect. Active shifts text to `ACCENT_ACTIVE`. No button chrome — the implant doesn't label its affordances.
+
+---
+
 *50 decisions. Last updated: 2026-03-24 (D-101 partial supersession noted; D-166 development cascade added)*