Make route navigation transactional

[nicodes]

Summary

• return explicit pending/succeeded/failed/superseded navigation results
• commit route, params, and history only after the matching mount succeeds
• use generation-aware threaded loading and cancellable transition completion
• dispose stale partial scenes and preserve state on failed back navigation
• document the breaking API and prepare v0.0.3

Part of aviorstudio/fieldsofrevik#152

Local acceptance evidence

• Godot 4.7.2.stable.official.ed1daf0bf
• GODOT_BIN=/tmp/opencode/godot-4.7.2/Godot_v4.7.2-stable_linux.x86_64 ./tests/test.sh — PASS, including six demonstrated negative controls and transactional routing regressions
• ./scripts/package_addon.py — PASS; ZIP SHA-256 5f850d789c5668a293d7d291d07e7a43932f947eeead03cf14da7798325b9a2a; installed tree SHA-256 3d0e949c9000529b1960e1a2d2c8fb6c301699c4e28a8c4893e4b967f65e8ed1; 36 files
• tests/package_lifecycle_test.sh — PASS; exact ZIP enable/restart/smoke/Web export/disable/restart and consumer-owned autoload preservation
• Playwright CLI 0.1.18 against the packaged Web export — PASS gd-router web_package_smoke reachable=1, 0 console errors
• Browser screenshot: to be uploaded as GitHub-hosted evidence after PR creation

No review requested: Team No Review workstream; coder-owned verification applies.

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[nicodes]

Correction — originating issue aviorstudio/fieldsofrevik#152: the initially published screenshot URL contained an unverified full commit suffix. It is corrected below to the verified exact head 18cba9c18e15bd3eda197a2bc3b22ec05e902789; the acceptance evidence itself is unchanged.

Self-verification evidence — exact head 18cba9c18e15bd3eda197a2bc3b22ec05e902789

Godot: 4.7.2.stable.official.ed1daf0bf; Playwright CLI: 0.1.18.

Acceptance criterion	Exact-head evidence
Transactional route/history commit and failed-back rollback	tests/hosted_router_test.gd: successful mounts commit route/params/history; missing-scene back returns FAILED and preserves route, params, and history. ./tests/test.sh passed.
Latest-wins explicit supersession (D03) and request generations	Overlapping deferred-host and real threaded-resource tests assert prior result SUPERSEDED, cancellation, stale completion rejection, and latest-only commit.
Transition/host lifecycle cleanup	Shared-transition overlap, invalid transition partial disposal, host destruction failure, externally freed previous scene, and abandoned threaded-load draining all passed without the new ObjectDB leak.
Repeated/concurrent regression coverage	Repeated push/replace/back and concurrent resource/transition cases passed in the canonical suite.
Exact assembled package/install lifecycle	./scripts/package_addon.py and tests/package_lifecycle_test.sh passed: 36 manifest files, ZIP SHA-256 5f850d789c5668a293d7d291d07e7a43932f947eeead03cf14da7798325b9a2a, installed-tree SHA-256 3d0e949c9000529b1960e1a2d2c8fb6c301699c4e28a8c4893e4b967f65e8ed1, enable/restart/smoke/Web export/disable/restart, consumer-owned autoload preserved.
Browser path	Playwright loaded the exact packaged Web export, observed PASS gd-router web_package_smoke reachable=1, and reported 0 console errors. Visual UI behavior itself is unchanged.
Exact-head CI	CI run 34718991598 completed successfully for the exact head.

Native stack linking remains blocked because gh stack link 11 12 is currently rejected by the caller account GraphQL quota; the PR base is correctly chained to a12-truthful-gates. No review requested or awaited under Team No Review.