docs: document Launcher Next mechanics and real P_Rec_Annot pilot

docs/architecture/autocad-startup.md

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+# AutoCAD startup
+
+Plant 3D 2026 is started with the confirmed contract:
+
+```text
+acad.exe /product PLNT3D /language ru-RU /b <absolute-local-script>
+```
+
+The generated script has one command:
+
+```text
+_.NETLOAD
+"<absolute local versioned PRecAnnot.Plant3D2026.dll>"
+```
+
+No `/p`, legacy LISP, `OrthoLoader`, UNC path, trusted-path mutation, or secondary dependency NETLOAD is used.

docs/architecture/package-activation.md

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+# Package activation
+
+Before changing package pointers, Launcher Next writes an activation snapshot containing exact previous `current.json` and `previous.json` contents and their SHA-256 values. Files are copied to a unique staging directory and rehashed. Only then is staging moved to `packages/<package>/versions/<version>` and the package-local pointer updated atomically.
+
+Rollback restores the exact pointers, deletes the pilot version and startup script, and removes incomplete staging. Autodesk assemblies, PDBs, executables, test assemblies and legacy files are rejected from the pilot package.

docs/architecture/pilot-state-machine.md

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+# Pilot state machine
+
+`Prepared → Activating → ProcessStarting → WaitingForRuntimeCheck → RolledBack`
+
+Failures are persisted as `Failed`. A new run is blocked by an active session; a completed `RolledBack` session permits a new run. `pilot rollback` restores state from its persisted activation snapshot and is repeatable.
+
+The current session schema persists the terminal state. It does not yet persist a transition-history array; evidence must not infer intermediate transitions after the fact.

docs/architecture/rollback-mechanics.md

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+# Rollback mechanics
+
+Rollback is performed only after the pilot-owned AutoCAD PID has exited. It restores pointer contents from the persisted snapshot, removes the generated SCR, cleans staging, deletes the activated pilot version, and writes session state `RolledBack`.
+
+If an application process exits unexpectedly, `pilot rollback` can be run in a new Launcher Next process because it reads the persisted session and activation snapshot.

docs/architecture/runtime-mechanics.md

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+# Launcher Next runtime mechanics
+
+The controlled pilot flow is: CLI `pilot run` → local `pilot.local.json` → manifest generation and SHA-256 validation → `PrepareAsync` → one-time in-memory permit → `ExecuteAsync` → staging → version activation → startup SCR → guarded `Process.Start` → wait for the specific AutoCAD PID → `RollbackAsync`.
+
+The pilot uses only `C:\AutoCAD User Support\LauncherNextPilot`. It does not modify the legacy launcher, AutoCAD profiles, registry, trusted paths, or the legacy Applications directory.
+
+The runtime command is `acad.exe /product PLNT3D /language ru-RU /b <startup-script>`; no profile argument is supplied. The SCR invokes exactly one `NETLOAD`, for the local versioned entry assembly only.