diff --git a/CHANGELOG.md b/CHANGELOG.md
index 10cd6b5..b01c68b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,42 @@ semantic versioning.
 
 ## [Unreleased]
 
+## [0.4.0] - 2026-11-06
+
+### Added
+
+- Two GUI display settings, at the foot of the window, hold for every plot and are remembered between launches: **Spectral axis** draws every spectral plot, maps and curves, against wavelength or frequency, with the density Jacobian, or keeps each on the axis it was computed on; **Log range** sets how far below its peak every logarithmic map reaches (5–120 dB). A map's colour bar can also be dragged to change that map's scale alone. Retrieve's own Spectrum axis control and Check's marginal axis control give way to them. `croak.plotting.display` does the conversion from a script.
+- Every plot and every page of the GUI can be saved as a figure for publication: a plot from its right-click menu (which can also save or copy it as an image), a page with "Export this page as a figure…" (Ctrl+E). Figures are drawn by matplotlib from the data on screen, at a single journal column per plot, as PDF, SVG or PNG; in a vector file the text stays editable and colour maps are rasterized. `croak.plotting.export` draws the same views from a script.
+- On Retrieve, once a retrieval is done, the top bar's primary action is **Analyse**, with **Retrieve again** beside it. Beneath the plots the run's numbers (iteration, error, elapsed time, the retrieved peak wavelength and FWHM, the forward-model extras and the truth errors) are shown large, beside the convergence curve, which follows the whole run; the pulse-parameter table is gone. Home's tiles carry drawings, and **Open a session** is a tile of its own.
+
+### Changed
+
+- The contributor workflow follows solprop's. `CONTRIBUTING.md` and the issue forms set
+  the standard for issues, labels and pull requests. A notable change now adds a
+  `changelog.d/` fragment instead of editing this file, and a rolling draft PR collects
+  the fragments after each merge. `poe check` also runs `codespell` and validates the
+  fragments. A new test keeps the version records in step, and `.zenodo.json` no longer
+  names a stale version. The workflows' actions are pinned by commit, and the release
+  checklist they refer to now exists in the Developer's guide.
+- The GUI has one way to save: **Save session…** now also writes what Analyse holds, the dispersed pulse (`result_dispersion.h5`, `dispersion.pdf`) when a dispersion is set and the uncertainty figure (`uncertainty.pdf`) when an estimate is on screen, and the Dispersion and Uncertainty pages lose their own Save… buttons. Prepare shows five numbers over its maps: the grid's size, time step, time window, wavelength span and the share of the trace its edge taper removes.
+- The GUI runs on PySide6 instead of PyQt6, and the `gui` extra now installs `pyside6-essentials`, `pyqtgraph` and `superqt`. Code that embeds croak's GUI widgets in its own Qt application must create a PySide6 `QApplication`.
+- Retrieve no longer has a ready line under its form: the numbers beneath its plots say how a run goes, its other messages are notices at the foot of the window, and a failed retrieval shows in the advice box over the plots. A slider's value box is now as wide as the numbers it takes, so the slider has the rest of the row, and a range has its two ends either side of one slider (TOD on the synthetic pulse page, among others, had a box wider than its slider).
+
+### Changed (breaking)
+
+- The GUI is redesigned as one workflow window in place of the six-step wizard: Home (start from a measured trace, a simulated scan or a synthetic pulse; open a session; recent sessions), then Data (load the trace), Check (its marginal), Prepare, Retrieve and Analyse (Overview, Traces, Pulse, Diagnostics, Dispersion and Uncertainty pages), with a Home button and one primary action in the top bar, an About page (version, links to the manual, GitHub and PyPI, authors and copyright), and the session's settings or a replay script on request. Plots are interactive pyqtgraph views with hover readouts, zoom and figure export through matplotlib; forms fold by section and say what the focused setting does. `croak.gui.run_wizard` is now `croak.gui.run_gui` and `croak.gui.Wizard` is now `croak.gui.MainWindow`; the `croak-gui` command is unchanged.
+
+### Removed
+
+- The matplotlib helpers that only the old GUI's live preview used are gone: `croak.plotting.RetrievalPageView`, `FrogFilterView`, the `update_*` panel functions (and `update_convergence_curve`), `PlotScale`, `plot_scale`, `scaled_rc` and their constants, and `PanelSpec.update`. The GUI draws on screen with pyqtgraph from the new `croak.plotting.screen` view data; the `draw_*` panels, `plot_retrieval`, `plot_retrieval_page`, `plot_frog_filter` and the other figures are unchanged.
+
+### Fixed
+
+- The GUI now says when the retrieval grid's λ range cuts off signal that is still in the trace: Prepare shows the share of the trace the edge taper removes and how to widen the range. The warning used to reach only the terminal.
+- The help for Retrieve's "Live full-plot preview" gives its real rate: up to four redraws a second, fewer when drawing is slow (it said about once a second).
+- The synthetic generator's spectrum preview is now a wavelength density, as its spectrogram already was.
+- A flat phase no longer fills its axis with rounding noise: phase axes span at least ±1 rad, in the GUI and in croak's figures.
+
 ## [0.3.1] - 2026-10-20
 
 ### Changed
@@ -690,7 +726,8 @@ Added in the run-up to the release:
   materials (missing `SiO2-Franta`); and `croak.solver`'s docstring described
   `Retriever` as the base of two solvers rather than of all of them.
 
-[Unreleased]: https://github.com/LupoLab/croak/compare/v0.3.1...HEAD
+[Unreleased]: https://github.com/LupoLab/croak/compare/v0.4.0...HEAD
+[0.4.0]: https://github.com/LupoLab/croak/compare/v0.3.1...v0.4.0
 [0.3.1]: https://github.com/LupoLab/croak/compare/v0.3.0...v0.3.1
 [0.3.0]: https://github.com/LupoLab/croak/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/LupoLab/croak/compare/v0.1.0...v0.2.0
diff --git a/CITATION.cff b/CITATION.cff
index 542e3c8..63cd83d 100644
--- a/CITATION.cff
+++ b/CITATION.cff
@@ -4,7 +4,7 @@ message: >-
   (preferred-citation below), and this record for the software itself.
 type: software
 title: "croak: complete retrieval of ultrashort laser pulses from FROG traces"
-version: 0.3.1
+version: 0.4.0
 authors:
   - family-names: Travers
     given-names: John C.
diff --git a/changelog.d/contributor-workflow.changed.md b/changelog.d/contributor-workflow.changed.md
deleted file mode 100644
index 9eb0961..0000000
--- a/changelog.d/contributor-workflow.changed.md
+++ /dev/null
@@ -1,7 +0,0 @@
-The contributor workflow follows solprop's. `CONTRIBUTING.md` and the issue forms set
-the standard for issues, labels and pull requests. A notable change now adds a
-`changelog.d/` fragment instead of editing this file, and a rolling draft PR collects
-the fragments after each merge. `poe check` also runs `codespell` and validates the
-fragments. A new test keeps the version records in step, and `.zenodo.json` no longer
-names a stale version. The workflows' actions are pinned by commit, and the release
-checklist they refer to now exists in the Developer's guide.
diff --git a/changelog.d/gui-display-settings.added.md b/changelog.d/gui-display-settings.added.md
deleted file mode 100644
index 41a51ea..0000000
--- a/changelog.d/gui-display-settings.added.md
+++ /dev/null
@@ -1 +0,0 @@
-Two GUI display settings, at the foot of the window, hold for every plot and are remembered between launches: **Spectral axis** draws every spectral plot, maps and curves, against wavelength or frequency, with the density Jacobian, or keeps each on the axis it was computed on; **Log range** sets how far below its peak every logarithmic map reaches (5–120 dB). A map's colour bar can also be dragged to change that map's scale alone. Retrieve's own Spectrum axis control and Check's marginal axis control give way to them. `croak.plotting.display` does the conversion from a script.
diff --git a/changelog.d/gui-figure-export.added.md b/changelog.d/gui-figure-export.added.md
deleted file mode 100644
index a3c16c0..0000000
--- a/changelog.d/gui-figure-export.added.md
+++ /dev/null
@@ -1 +0,0 @@
-Every plot and every page of the GUI can be saved as a figure for publication: a plot from its right-click menu (which can also save or copy it as an image), a page with "Export this page as a figure…" (Ctrl+E). Figures are drawn by matplotlib from the data on screen, at a single journal column per plot, as PDF, SVG or PNG; in a vector file the text stays editable and colour maps are rasterized. `croak.plotting.export` draws the same views from a script.
diff --git a/changelog.d/gui-matplotlib-live-preview.removed.md b/changelog.d/gui-matplotlib-live-preview.removed.md
deleted file mode 100644
index 3693026..0000000
--- a/changelog.d/gui-matplotlib-live-preview.removed.md
+++ /dev/null
@@ -1 +0,0 @@
-The matplotlib helpers that only the old GUI's live preview used are gone: `croak.plotting.RetrievalPageView`, `FrogFilterView`, the `update_*` panel functions (and `update_convergence_curve`), `PlotScale`, `plot_scale`, `scaled_rc` and their constants, and `PanelSpec.update`. The GUI draws on screen with pyqtgraph from the new `croak.plotting.screen` view data; the `draw_*` panels, `plot_retrieval`, `plot_retrieval_page`, `plot_frog_filter` and the other figures are unchanged.
diff --git a/changelog.d/gui-one-save.changed.md b/changelog.d/gui-one-save.changed.md
deleted file mode 100644
index e143161..0000000
--- a/changelog.d/gui-one-save.changed.md
+++ /dev/null
@@ -1 +0,0 @@
-The GUI has one way to save: **Save session…** now also writes what Analyse holds, the dispersed pulse (`result_dispersion.h5`, `dispersion.pdf`) when a dispersion is set and the uncertainty figure (`uncertainty.pdf`) when an estimate is on screen, and the Dispersion and Uncertainty pages lose their own Save… buttons. Prepare shows five numbers over its maps: the grid's size, time step, time window, wavelength span and the share of the trace its edge taper removes.
diff --git a/changelog.d/gui-prepare-taper-advice.fixed.md b/changelog.d/gui-prepare-taper-advice.fixed.md
deleted file mode 100644
index 3435070..0000000
--- a/changelog.d/gui-prepare-taper-advice.fixed.md
+++ /dev/null
@@ -1 +0,0 @@
-The GUI now says when the retrieval grid's λ range cuts off signal that is still in the trace: Prepare shows the share of the trace the edge taper removes and how to widen the range. The warning used to reach only the terminal.
diff --git a/changelog.d/gui-preview-help.fixed.md b/changelog.d/gui-preview-help.fixed.md
deleted file mode 100644
index 116d28a..0000000
--- a/changelog.d/gui-preview-help.fixed.md
+++ /dev/null
@@ -1 +0,0 @@
-The help for Retrieve's "Live full-plot preview" gives its real rate: up to four redraws a second, fewer when drawing is slow (it said about once a second).
diff --git a/changelog.d/gui-pyside6.changed.md b/changelog.d/gui-pyside6.changed.md
deleted file mode 100644
index 99908b5..0000000
--- a/changelog.d/gui-pyside6.changed.md
+++ /dev/null
@@ -1 +0,0 @@
-The GUI runs on PySide6 instead of PyQt6, and the `gui` extra now installs `pyside6-essentials`, `pyqtgraph` and `superqt`. Code that embeds croak's GUI widgets in its own Qt application must create a PySide6 `QApplication`.
diff --git a/changelog.d/gui-retrieve-notices.changed.md b/changelog.d/gui-retrieve-notices.changed.md
deleted file mode 100644
index 10c3d57..0000000
--- a/changelog.d/gui-retrieve-notices.changed.md
+++ /dev/null
@@ -1 +0,0 @@
-Retrieve no longer has a ready line under its form: the numbers beneath its plots say how a run goes, its other messages are notices at the foot of the window, and a failed retrieval shows in the advice box over the plots. A slider's value box is now as wide as the numbers it takes, so the slider has the rest of the row, and a range has its two ends either side of one slider (TOD on the synthetic pulse page, among others, had a box wider than its slider).
diff --git a/changelog.d/gui-retrieve-strip.added.md b/changelog.d/gui-retrieve-strip.added.md
deleted file mode 100644
index b1cc870..0000000
--- a/changelog.d/gui-retrieve-strip.added.md
+++ /dev/null
@@ -1 +0,0 @@
-On Retrieve, once a retrieval is done, the top bar's primary action is **Analyse**, with **Retrieve again** beside it. Beneath the plots the run's numbers (iteration, error, elapsed time, the retrieved peak wavelength and FWHM, the forward-model extras and the truth errors) are shown large, beside the convergence curve, which follows the whole run; the pulse-parameter table is gone. Home's tiles carry drawings, and **Open a session** is a tile of its own.
diff --git a/changelog.d/gui-signed-map-noise.fixed.md b/changelog.d/gui-signed-map-noise.fixed.md
deleted file mode 100644
index d36c5d4..0000000
--- a/changelog.d/gui-signed-map-noise.fixed.md
+++ /dev/null
@@ -1 +0,0 @@
-A signed linear map in the GUI no longer paints its whole zero background red when its only negative values are rounding noise (Prepare's filtered and regridded traces), and the synthetic generator's spectrum preview is now a wavelength density, as its spectrogram already was. Log axes are labelled at decades only, so a short convergence plot no longer piles its labels up.
diff --git a/changelog.d/gui-synthetic-preview.fixed.md b/changelog.d/gui-synthetic-preview.fixed.md
deleted file mode 100644
index 2c3a950..0000000
--- a/changelog.d/gui-synthetic-preview.fixed.md
+++ /dev/null
@@ -1 +0,0 @@
-The synthetic generator's trace preview shows the trace that Continue hands on, sampled onto the λ window; it used to show a featureless stripe. A flat phase no longer fills its axis with rounding noise: phase axes span at least ±1 rad, in the GUI and in croak's figures.
diff --git a/changelog.d/gui-workflow-window.breaking.md b/changelog.d/gui-workflow-window.breaking.md
deleted file mode 100644
index 8788ad2..0000000
--- a/changelog.d/gui-workflow-window.breaking.md
+++ /dev/null
@@ -1 +0,0 @@
-The GUI is redesigned as one workflow window in place of the six-step wizard: Home (start from a measured trace, a simulated scan or a synthetic pulse; open a session; recent sessions), then Data (load the trace), Check (its marginal), Prepare, Retrieve and Analyse (Overview, Traces, Pulse, Diagnostics, Dispersion and Uncertainty pages), with a Home button and one primary action in the top bar, an About page (version, links to the manual, GitHub and PyPI, authors and copyright), and the session's settings or a replay script on request. Plots are interactive pyqtgraph views with hover readouts, zoom and figure export through matplotlib; forms fold by section and say what the focused setting does. `croak.gui.run_wizard` is now `croak.gui.run_gui` and `croak.gui.Wizard` is now `croak.gui.MainWindow`; the `croak-gui` command is unchanged.
diff --git a/croak/__init__.py b/croak/__init__.py
index 5928afb..a5a4675 100644
--- a/croak/__init__.py
+++ b/croak/__init__.py
@@ -253,4 +253,4 @@
     "ALGORITHMS",
     "RetrievalResult",
 ]
-__version__ = "0.3.1"
+__version__ = "0.4.0"
diff --git a/pyproject.toml b/pyproject.toml
index 0a1beb8..14cb067 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "croak"
-version = "0.3.1"
+version = "0.4.0"
 description = "Complete retrieval of ultrashort laser pulses from FROG traces — amplitude and phase, with dispersive media, geometric smearing and uncertainty"
 readme = "README.md"
 requires-python = ">=3.14"
diff --git a/uv.lock b/uv.lock
index 6b30339..cb22c61 100644
--- a/uv.lock
+++ b/uv.lock
@@ -304,7 +304,7 @@ wheels = [
 
 [[package]]
 name = "croak"
-version = "0.3.1"
+version = "0.4.0"
 source = { editable = "." }
 dependencies = [
     { name = "finufft" },