diff --git a/docs/adr/0113-shared-renderer-attachment-path-normalization.md b/docs/adr/0113-shared-renderer-attachment-path-normalization.md
new file mode 100644
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@@ -0,0 +1,43 @@
+---
+type: ADR
+id: "0113"
+title: "Shared renderer attachment path normalization"
+status: active
+date: 2026-05-07
+---
+
+## Context
+
+Tolaria already treats vault attachments as ordinary files under `attachments/`, and ADRs around previews and asset scoping rely on Tauri asset URLs to render them safely. In practice, attachment handling had started to fragment across the renderer: some flows joined `vaultPath + attachments/...`, some decoded `convertFileSrc` URLs directly, some handled Windows separators ad hoc, and some only worked for one editor surface.
+
+That duplication turned attachment behavior into a drift risk. Opening file blocks, following editor links, serializing raw-mode Markdown, rewriting image URLs after vault switches, and copying dropped files into the vault all needed the same three representations to stay in sync:
+
+- portable markdown references such as `attachments/report.pdf`
+- Tauri asset URLs used by the renderer
+- absolute filesystem paths inside the active vault
+
+## Decision
+
+**Tolaria centralizes attachment path conversion in a single renderer-owned primitive and keeps portable `attachments/...` references as the canonical cross-surface representation.**
+
+Specifically:
+
+1. `src/utils/vaultAttachments.ts` is the single owner for converting between portable attachment references, Tauri asset URLs, and active-vault filesystem paths.
+2. Editor rendering, raw-mode serialization, image upload/drop flows, file-block open actions, and parsed-media cleanup must call that shared primitive instead of carrying local path/URL conversion logic.
+3. Renderer code may derive absolute paths only relative to the current active vault and must reject asset URLs or relative paths that fall outside that boundary.
+4. Tauri asset URLs remain a transport/rendering detail, not a persisted vault format.
+
+## Alternatives considered
+
+- **Shared renderer attachment-path primitive with portable persisted refs** (chosen): keeps behavior consistent across media rendering, editor actions, and vault switching while preserving Markdown portability.
+- **Per-feature helpers for each attachment surface**: simpler locally, but repeats Windows/path-normalization rules and lets editor actions drift apart.
+- **Persist absolute paths or Tauri asset URLs in Markdown/editor state**: would couple notes to one machine or one runtime session and make vault content less portable.
+- **Push all attachment conversion into backend commands**: could reduce renderer logic, but the renderer still needs a shared local model for in-memory markdown rewriting, link activation, and preview URL handling.
+
+## Consequences
+
+- Attachment behavior becomes consistent across previews, editor links, toolbar/file-block opens, drag-drop imports, and markdown serialization.
+- Vault content stays portable because persisted references remain `attachments/...` paths rather than machine-specific absolute paths or session-specific asset URLs.
+- Cross-platform edge cases such as Windows separators, encoded asset URLs, and vault-switch rewrites now have one place to harden and test.
+- The Rust command layer remains the write/read security boundary; this ADR only centralizes renderer-side normalization before those commands are called or asset URLs are rendered.
+- Future attachment/media features should extend `vaultAttachments.ts` rather than introducing new ad hoc conversion helpers.
diff --git a/docs/adr/README.md b/docs/adr/README.md
index 0a674fc5..6ff10c49 100644
--- a/docs/adr/README.md
+++ b/docs/adr/README.md
@@ -166,3 +166,4 @@ proposed → active → superseded
 | [0110](0110-in-app-media-and-pdf-file-previews.md) | In-app media and PDF previews for binary vault files | active |
 | [0111](0111-path-aware-external-vault-refresh-with-focused-editor-preservation.md) | Path-aware external vault refresh with focused-editor preservation | active |
 | [0112](0112-system-theme-mode.md) | System theme mode | active |
+| [0113](0113-shared-renderer-attachment-path-normalization.md) | Shared renderer attachment path normalization | active |