diff --git a/README.md b/README.md
index e9c66dc..99425e5 100644
--- a/README.md
+++ b/README.md
@@ -1,17 +1,18 @@
 # lib-core.input
 
 P.0 action-mapping lib. Decouples physical keys from logical actions.
-Polling-based (`is_action_down`) + edge-based (`was_action_pressed`).
+Polling-based (`is_action_down`) + edge-based (`was_action_pressed`, `was_action_released`).
 Direction-vector helper composes 4 actions into `{x, y}` ∈ {-1, 0, +1}².
 
 - Lib-ID: `lib-core.input`
-- Version: `0.2.0` (breaking change from v0.1.0 — string-keys only, see §Migration)
+- Version: `0.4.0`
+- Spec v0.3.0 (P.3.3): `meta/docs/superpowers/specs/2026-05-12-p3-3-mouse-input-design.md`
 - Spec v0.2.0 (P.2.6): `meta/docs/superpowers/specs/2026-05-11-engine-input-symbolic-keys-design.md`
 - Spec v0.1.0 (P.0): `meta/docs/superpowers/specs/2026-05-09-p0-lib-input-design.md`
 
 Forward-compat stubs (DEPRECATED-MVP) for mouse-button actions, gamepad
 bindings, action-context-stack, key-rebinding-config, modifier-combos,
-analog-axis, was_action_released edge, right-modifier-keys, function-keys,
+analog-axis, right-modifier-keys, function-keys,
 special-keys (delete/insert/home/end/pageup/pagedown).
 
 ## API
@@ -19,7 +20,8 @@ special-keys (delete/insert/home/end/pageup/pagedown).
 - `input.bind(action_name, {"keyname1", "keyname2", ...})` — bind multi-key array (string-keys only, see §Key-Names)
 - `input.unbind(action_name)` — remove binding
 - `input.is_action_down(action) → bool` — any bound key currently down
-- `input.was_action_pressed(action) → bool` — any bound key just-pressed
+- `input.was_action_pressed(action) → bool` — any bound key just-pressed (press-edge; true for exactly one frame per key-down event)
+- `input.was_action_released(action) → bool` — any bound key just-released (release-edge; true for exactly one frame per key-up event; triggers once per press-release cycle)
 - `input.direction(left, right, up, down) → {x, y}` — vec in {-1,0,+1}², Y-down-positive
 - `input.action_count() → number` — bound-actions count
 
@@ -74,3 +76,18 @@ end
 | `bind("move", { engine.input.KEY_A, engine.input.KEY_LEFT })` | `bind("move", { "a", "left" })` |
 
 `engine.input.KEY_*` constants remain available for direct engine-input use (e.g. `engine.input.is_key_down(engine.input.KEY_F1)` for edge-cases without bind), but `lib-core.input.bind` strict-rejects them.
+
+## CHANGELOG
+
+## v0.4.0 (P.3.10, 2026-05-15)
+- Added `was_action_released(action_name)` — release-edge detection per action.
+  Selection-Lib's `prev_click_down` workaround promoted.
+- Engine surface: `engine.input.was_released` + `was_mouse_released`.
+
+## v0.3.0 (P.3.3, 2026-05-12)
+- `bind()` now accepts unified key+mouse strings via BIND_MAP with kind-tagged entries.
+- Mixed bindings supported (e.g. `{"e", "mouse_left"}`).
+- Backward-compatible with v0.2.0 callsites.
+
+## v0.2.0 (P.2.6, 2026-05-11)
+- `bind()` accepts string-key-names only. Integer `engine.input.KEY_*` args are rejected.
diff --git a/init.lua b/init.lua
index 5e27307..64e80c8 100644
--- a/init.lua
+++ b/init.lua
@@ -1,7 +1,12 @@
 -- =====================================================================
--- lib-core.input — Action-Mapping + Direction-Vector (v0.3.0)
+-- lib-core.input — Action-Mapping + Direction-Vector (v0.4.0)
 -- See: meta/docs/superpowers/specs/2026-05-12-p3-3-mouse-input-design.md
 --
+-- v0.4.0 (P.3.10 2026-05-15): was_action_released added — release-edge
+-- detection parallel to was_action_pressed. Engine-Surface:
+-- engine.input.was_released + was_mouse_released. Selection-Lib's
+-- prev_click_down workaround promoted.
+--
 -- v0.3.0 (P.3.3 2026-05-12): bind() now accepts unified key+mouse
 -- strings via BIND_MAP with kind-tagged entries ({kind="key"|"mouse",
 -- code=<engine-int>}). Mixed bindings supported: e.g.
@@ -12,10 +17,10 @@
 -- v0.2.0 (P.2.6 2026-05-11): bind() accepts string-key-names only.
 -- Integer engine.input.KEY_* args are rejected.
 --
--- Scope v0.3.0: action-mapping (string-key+mouse-arrays per action) +
--- direction-vector helper. DEPRECATED-MVP: mouse-wheel, was_released
--- edge, mouse-delta helper, side-buttons, gamepad bindings,
--- action-context-stack, key-rebinding config.
+-- Scope v0.4.0: action-mapping (string-key+mouse-arrays per action) +
+-- press-edge + release-edge detection + direction-vector helper.
+-- DEPRECATED-MVP: mouse-wheel, mouse-delta helper, side-buttons,
+-- gamepad bindings, action-context-stack, key-rebinding config.
 -- =====================================================================
 
 -- Unified string → {kind, code} mapping. Lowercase convention.
@@ -126,6 +131,16 @@ function M.was_action_pressed(action_name)
     return false
 end
 
+function M.was_action_released(action_name)
+    local entries = bindings[action_name]
+    if not entries then return false end
+    for _, e in ipairs(entries) do
+        if e.kind == "key"   and engine.input.was_released(e.code)       then return true end
+        if e.kind == "mouse" and engine.input.was_mouse_released(e.code) then return true end
+    end
+    return false
+end
+
 -- Direction-vector helper: returns {x, y} in {-1, 0, +1} each axis.
 -- Y-down-positive per Sporel pixel-convention (ADR-0031).
 function M.direction(left_action, right_action, up_action, down_action)
@@ -144,7 +159,6 @@ end
 
 -- DEPRECATED-MVP (P.3.3-introduced):
 -- mouse-wheel binding (wheel_up/wheel_down) — P.3-future-slice (post-P.3.4); continuous-vs-edge brainstorming needed
--- was_action_released(action) — lift-detection-edge (both key + mouse atomic)
 -- mouse-delta helper (engine.input.get_mouse_delta) — P.3.5/6 drag-pan / drag-box
 -- mouse-button side-buttons (mouse_4 / mouse_5) — additive extension
 -- mouse-position lib-wrapper (input.mouse_pos() → {x,y}) — convenience layer
diff --git a/manifest.lib b/manifest.lib
index f2cb25a..baae2ef 100644
--- a/manifest.lib
+++ b/manifest.lib
@@ -1 +1 @@
-{"id":"lib-core.input","version":"0.3.0","api_min":"0.1"}
+{"id":"lib-core.input","version":"0.4.0","api_min":"0.1"}
\ No newline at end of file