[MendixMau]

Closes #1782.

What

Adds mxcli test --reuse-build. On a repeat mxcli test run, if the project
tree, the generated test-endpoint/test-microflow MDL, the mxcli executable
and the mxbuild path/flags all hash to the same key as the build currently
on disk (pinned to deployment/model/model.mdp's identity so a build made
by anything else is never mistaken for ours), skip injection and the
mxbuild rebuild and boot straight from the existing deployment/.
--constant values are runtime configuration, not model, so different
constants don't invalidate reuse.

Why

Repeat mxcli test runs during iterative test-writing pay a full
inject+mxbuild+boot cycle every time, even when only a test file changed
and the model is untouched.

Real-app numbers (with denominators)

Measured against a copy of a real ~280MB Mendix app
(~/mta-lab/w/r1test, 14 tests across 3 .test.mdl files), machine load
noted at each measurement (1-minute load average). An earlier pass on this
same app was re-run after it turned out that pass had not recorded load,
and the machine was later found to be running at load 44-58 from unrelated
concurrent sessions during parts of this work — the numbers below are the
re-confirmed ABAB set, captured while load was climbing back from a 13.38
trough (13-32 band throughout, well below the 44-58 band seen elsewhere):

run	time	load (1-min avg, start)
full rebuild (no --reuse-build)	96s	15.5
full rebuild (forced stale-model rebuild)	66s	24.6
--reuse-build, no build recorded yet (builds)	66s	26.4
--reuse-build steady-state hit	12s	21.7
--reuse-build steady-state hit (repeat)	12s	20.8

5.5x reduction (66s rebuild vs 12s reuse hit) in the "I changed a test, not
the model" loop, 14/14 green on every run.

A real bug found and fixed during this work

The first working version did not exclude theme-cache/ from the hashed
project tree. mxbuild rewrites theme-cache/web/theme.compiled.css on
every build with a non-deterministic cache-busting query string on every
font/asset url() (Atlas_Styling.ttf?<token>), even with zero theme or
model change. Because that file lives inside the project tree, it was
counted as a build input — so the hash key never repeated across two
separate mxcli test invocations on any app using the Atlas Core theme
(effectively all of them), and --reuse-build was a complete no-op on real
apps despite passing synthetic unit tests. Fixed by adding theme-cache to
the skip-dir set; re-verified on the real app (12.15s reuse hit vs the prior
~60-67s miss on every single call).

How it was tested

• 12 unit tests, cmd/mxcli/testrunner/reusebuild_test.go:
  go test ./cmd/mxcli/testrunner/... -run 'TestHashProjectTree|TestReusableBuild|TestTestBuildKey|TestForgetBuild|TestRecordBuild' -v → all PASS.
• Real-app A/B timings above.
• 5 negative controls against the real app (4 applicable to this change's
  scope):
  1. Wrong @expect → red; --reuse-build of that build stays red;
     restoring the file → rebuild, green.
  2. Seeded model bug (an attribute guard removed) → rebuild red on the
     affected test; --reuse-build reuses that red build, stays red;
     reverting the bug → rebuild, green.
  3. Broken model (microflow missing a required return) → build fails
     cleanly, never reports a pass.
  4. Stale model via an independent touch of deployment/model/model.mdp
     → correctly detected as stale (identity mismatch), falls back to a
     full rebuild.
  5. Rollback-leaves-0-rows: not applicable — this flag only decides
     whether to skip inject+build+boot; it never touches
     execution/assertion/rollback behavior.

Known limitation (not a bug)

Interleaving a plain (non---reuse-build) run between two --reuse-build
runs invalidates the chain: the plain run's own inject-then-cleanup
round-trip changes the project tree enough that the following
--reuse-build call correctly (safely) misses and rebuilds — the intended
fail-safe, but it means strict alternation between the two modes never
shows the steady-state number, only sustained --reuse-build use does.

Checklist (CONTRIBUTING.md)

• make build succeeds
• make lint passes
• make test — unit tests for the touched package pass; full-repo
  suite run is in progress (will update before marking ready for
  review)
• Mendix Studio Pro validation — not applicable: this change affects
  only mxcli's own test-runner build-reuse decision, not generated MDL,
  BSON serialization, or any entity/microflow model shape
• One concern per PR

Marked as draft until the full make test run is confirmed green and
CI passes.

🤖 Generated with Claude Code