fix(repl): set_evaluator() alone should open the Repl tab

[martin-henz]

Summary

Reported repro:

from repl import set_evaluator
from rune import show, heart

def dummy(code):
    pass

set_evaluator(dummy)

No Repl tab appears. This is not rune-related (show/heart are imported but never called, so rune's tab correctly staying hidden is expected) - it reproduces with repl alone.

Root cause

ReplModulePlugin.set_evaluator (src/bundles/repl/src/index.ts) never called the private lazy tab-loader __loadReplTab(). Every other function that gives a student a reason to look at the tab already does (set_program_text, repl_display/rich_repl_display via __displayOutput, set_background_image/set_font_size via __displayEditorProps) - set_evaluator was the one exception, missed when this lazy-load pattern was introduced during the Conductor migration (#865).

Since the tab is only ever constructed via that loader, a program whose only interaction with the module is set_evaluator() - exactly the module's own documented minimal usage example in the file's module doc comment - never opened the tab at all.

Fix

set_evaluator now calls this.__loadReplTab() after registering the evaluator, matching the existing pattern used by every other tab-opening method.

Test plan

• yarn tsc and yarn lint pass for src/bundles/repl and src/tabs/Repl
• Existing test suites pass (43 bundle tests, 12 tab tests) - unaffected
• Verified the compiled bundle output directly: set_evaluator now calls __loadReplTab() (4 call sites total, up from 3)
• Could not add a unit test asserting this directly in the usual style (tabLoader.loadTab called after set_evaluator()) - vitest's transform currently fails to import the plugin class (index.ts) for any bundle using the newer "standard decorators" syntax (binary_tree, matrix, midi, pix_n_flix, repeat, repl, sound). This is a pre-existing tooling gap, not something new from this change - none of those bundles currently have a test importing their own index.ts. Flagging in case it's worth a separate look.

🤖 Generated with Claude Code

https://claude.ai/code/session_01B3LRoXRMQ5ADeYMdVTChCZ

[gemini-code-assist]

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