fix: add margin around modules when zooming (#61)

[charlesangus]

Closes #61.

Problem

Navigating to a module (an anchor plus its upstream nodes) framed the nodes edge-to-edge with no breathing room. Backdrops, by contrast, look well-framed because the backdrop node is physically larger than its contents, leaving natural margin.

Root cause

navigate_to_anchor() selects the module nodes and calls nuke.zoomToFitSelected(), which fits the selection's bounding box to fill the viewport with no padding. Nuke's API exposes no margin/padding parameter for that call.

Fix

Apply the margin as a post-fit zoom-out. After zoomToFitSelected(), read the resulting scale and center and re-zoom by a factor:

fitted_scale = nuke.zoom()
fitted_center = nuke.center()
nuke.zoom(fitted_scale * MODULE_ZOOM_MARGIN_FACTOR, fitted_center)

MODULE_ZOOM_MARGIN_FACTOR = 0.85 (new constant in constants.py) leaves ~7.5% of the viewport as margin on each side — roughly 100–200px on a typical DAG panel, matching the issue request — and adapts to any panel size rather than hard-coding a pixel count.

Alternatives considered

• Fixed-pixel margin via Qt viewport query: would honor "100–200px" literally, but requires locating the DAG QWidget reliably across Nuke versions/docked panels and is much harder to unit-test. The proportional factor lands in the requested range with far less fragility.

Tests

• test_zooms_out_for_margin_after_fit — verifies a single re-zoom at fitted_scale * MODULE_ZOOM_MARGIN_FACTOR with the fitted center.
• test_margin_zoom_out_happens_after_fit — verifies ordering (fit first, margin zoom-out last).
• setUp/tearDown hardened to reset shared zoom mocks so the new side_effects don't leak across test classes.

Full suite: 484 passed.

UAT

Pending — to be performed in Nuke by the maintainer (navigate to a module via Alt+A / leader key; confirm visible margin; confirm back-navigation and link-cycling still work).

[Copilot]

Pull request overview

This PR fixes overly tight framing when navigating to a module (anchor + upstream nodes) by adding post-fit “breathing room” around the selection, matching the nicer framing users see with backdrops.

Changes:

• Add a new MODULE_ZOOM_MARGIN_FACTOR constant to apply proportional zoom-out margin after nuke.zoomToFitSelected().
• Update navigate_to_anchor() to re-zoom after fitting using the fitted zoom + center as a baseline.
• Extend navigation tests to verify the margin zoom-out behavior and ensure zoom/fit mocks don’t leak side_effects across tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
anchor.py	Applies a post-zoomToFitSelected() zoom-out using fitted zoom/center to create module margin.
constants.py	Introduces MODULE_ZOOM_MARGIN_FACTOR = 0.85 with rationale and framing notes.
tests/test_anchor_navigation.py	Adds tests for margin zoom-out behavior and hardens mock reset/cleanup to prevent leakage.

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