shopdb-flask/docs/proposals/device-identity.md

# Proposal: one identity for the device a PC drives, ending in the registry

Status: PHASE 1 DONE (shipped after 0.12.0). Phases 2 and 3 not started.
Author: planning session 2026-08-20.

## 1. What this is

A shop-floor PC often drives something: a CMM, a Keyence, a Genspect, a
wax-trace unit, a part marker. ShopDB needs to know WHICH one, and the answer
has to survive the PC being replaced.

Today that answer is assembled from whatever each bay family happens to have,
and two of the three sources are derived from the PC itself, so they do not
survive a swap. This proposal converges them on one identity, moves it from
files to the registry, and does it in three phases so no bay is stranded.

## 2. Why PC-derived identity fails

Two mechanisms stand in for a real identity today:

- **Reuse**: look for a prior collector link from THIS PC asset.
- **Mint**: build `<PC assetnumber>-<SUFFIX>`, and a PC's asset number is its
  hostname.

Both survive a re-image. Neither survives a PC SWAP. A new hostname is a new PC
asset with no prior link and a predicted number that has never existed, so the
same physical device gets a SECOND record while the first keeps its config and
its backup history under a dead PC's name.

That is not hypothetical: minting from the hostname left 43 legacy `MT-####`
tools shadowed by minted twins, three records deep in places.

## 3. The rail that must not be crossed

`machinenumber` answers "WHICH BAY is this" and is what GE-Enforce
`TargetMachineNumbers` gates on. The device identity answers "WHICH DEVICE is
this". They are different facts and must stay in different fields.

Putting a device id into the machine-number channel would silently stop every
bay-gated manifest entry from matching - a failure that looks like nothing
happening, on every cycle, with no error anywhere.

## 4. Where identity comes from today

| Bay family | Identity source | Survives a PC swap |
|---|---|---|
| DNC / collections | `MachineNo` in the eDNC/NTLARS registry | yes |
| CMM | `C:\Enrollment\cmm\cmmid.txt` | yes, but see below |
| Keyence, Genspect, wax-trace | nothing, before phase 1 | no |
| Part markers | nothing, before phase 1 | no |

**`cmmid.txt` is not only an identity file.** It is a PATH KEY, and that is why
it cannot simply be retired:

| Consumer | Use |
|---|---|
| `resolve-cmm-bay-config.ps1` | writes it |
| `Verify-And-Heal-Staging.ps1` | stages `installers-post\cmm\backups\<cmmid>` |
| `09-Setup-CMM.ps1` | locates the bay's staged backup set |
| `Restore-CMM.ps1` | restores from `<BackupRoot>\<cmmid>\`, same-bay by design |
| collector | reads it as `machineNo` |

Only the last row is an identity use. The rest address directories by it.

It is also doing the job badly: for a CMM bay it reports the INSTRUMENT's id in
the `machinenumber` channel, and the server then resolves it back to a measuring
tool at step 4 of its own fallback chain. That round trip is what phases 2 and 3
remove.

## Phase 1 - one field, one file (DONE)

The collector accepts a single `deviceid`, read from `C:\Enrollment\asset-id.txt`
and resolved BEFORE anything PC-derived, for every device family.

- One file for every bay with no `MachineNo` registry to identify it.
- It names the asset and NOT its type: the pc-type already says what kind of
  device it is, through `SUBORDINATE_DEVICE_MAP`, so a device type declared
  later through `subordinatedevice_<pctype>` needs no new file and no client
  change.
- Wire field is `deviceid`, not `assetid`, because `assetid` is already this
  contract's RESPONSE field for a PC's integer primary key.
- `measuringtoolid` (0.12.0) is accepted as an alias and the older file is still
  read, so a bay staged in that window keeps reporting.
- Guards: an unresolvable value warns rather than minting a phantom, and a value
  resolving to the WRONG KIND of asset is refused with the asset named.

Nothing was removed. Every previous fallback still runs, one place lower.

## Phase 2 - imaging writes it, and `cmmid.txt` stops being an identity

Repository: the PXE/imaging repo, not this one. **Needs deploying to the live
server, not only committing** - the live boot image is authoritative.

1. `resolve-cmm-bay-config.ps1` writes `C:\Enrollment\asset-id.txt` ALONGSIDE
   `cmmid.txt`. Two files, two questions: the identity, and the backup-set key.
   `cmmid.txt` keeps every path use it has today.
2. Every other device pc-type writes `asset-id.txt` at imaging from its bay
   config. Bays with no device write nothing, and the file's absence stays
   meaningful.
3. The collector demotes `cmmid.txt` to last place in the machine-number chain
   and stops being the intended path for CMM identity. It is still read, so a
   grandfathered bay that never gets re-imaged keeps reporting.
4. The value written is the device's `assetnumber` as ShopDB holds it. Where a
   CMM's asset number is already its bay id (`CMM3`), phase 2 is a no-op in
   content and a change only in which file carries it.

Exit criterion: a report from a re-imaged bay of each device family carries
`deviceid`, and no bay of those families relies on the `cmmid.txt` fallback.
The collector response warnings are the check: an adopted device is silent, a
minted one is not.

## Phase 3 - identity moves to the registry

`HKLM:\SOFTWARE\GE\ShopDB\DeviceId`.

This is the destination because the registry survives the profile cleanup and
disk hygiene that eats `C:\Enrollment`, is readable as SYSTEM with no file ACL
to get wrong, and is already how a DNC bay is identified. It needs no new key
and no new read path: the collector already opens
`HKLM:\SOFTWARE\GE\ShopDB` (and the `WOW6432Node` variant) for `BaseUrl` and
`ApiToken`, and `Install-GEEnforce.ps1` already writes that key.

**One value, every family.** `DeviceId` is a single registry value, not a key
per device type. The client sends one field and the pc-type decides which sync
consumes it, exactly as `asset-id.txt` works in phase 1, so:

| Bay | `DeviceId` holds | Replaces |
|---|---|---|
| CMM | the instrument's `assetnumber` | `cmmid.txt` as IDENTITY only |
| Keyence | the instrument's `assetnumber` | nothing; had none |
| Genspect | the instrument's `assetnumber` | nothing; had none |
| wax-trace | the instrument's `assetnumber` | nothing; had none |
| part marker | the marker's `assetnumber` | minting from the hostname |

A device family added later through `subordinatedevice_<pctype>` is covered on
the day it is declared, with no client change and no new registry value.

Resolution order after phase 3:

1. `HKLM:\SOFTWARE\GE\ShopDB\DeviceId`
2. `C:\Enrollment\asset-id.txt`
3. `C:\Enrollment\measuringtool-id.txt` (0.12.0 window)
4. `C:\Enrollment\cmm\cmmid.txt` as `machineNo` (grandfathered CMM bays)

Then, and only then, the file branches can be deleted one at a time, newest
first, each when no bay has reported through it for a full inventory cycle.

**`cmmid.txt` survives phase 3 regardless**, as the CMM backup-set path key. It
is not on the deletion list; only its identity use is.

### PXE and GE-Enforce prefer it too, not just the collector

Phase 3 is not only "the collector reads a registry value". All three writers
and readers move together:

| Component | Change |
|---|---|
| PXE / imaging | writes `DeviceId` at enrollment instead of (or as well as) the file |
| GE-Enforce | resolves device identity registry-first, mirroring how it already resolves the machine number |
| collector | reads the registry ahead of the file |

**GE-Enforce already made this exact decision for the machine number, and wrote
down why.** `Install-FromManifest.ps1` resolves `TargetMachineNumbers` gating
from the eDNC registry BEFORE `C:\Enrollment\machine-number.txt`, because:

> the imaging-time `machine-number.txt` is written ONCE by `startnet.cmd` at the
> PXE menu and is NOT updated on reassignment, so it goes stale.

**`asset-id.txt` inherits that defect exactly.** It is written once at imaging
and nothing updates it when a device is swapped, moved between bays, or
replaced. The bay then reports an identity that was true on imaging day, and the
collector - which now trusts that value FIRST, ahead of every other source -
adopts the wrong device with no warning, because the value still resolves.

That makes phase 3 a correctness fix rather than a tidy-up. A file that only
imaging writes cannot be the top of a resolution order for something that
changes during a PC's life.

It also implies a reassignment path, the way `Set-MachineNumber` /
`Update-MachineNumber` exist for the bay number: something that rewrites
`DeviceId` when a device is swapped, and migrates any per-device state with it.
Without that, phase 3 moves the staleness from a file to a registry value rather
than curing it.

### Doing phase 3 early is cheaper than doing it late

If the registry read lands before imaging is changed, phase 2 can write the
REGISTRY for new bays and skip the file era entirely for them. The file then
exists only for bays staged in the window between phase 1 and phase 2, and the
eventual cleanup is deleting a code branch rather than sweeping the fleet.

The cost of adding the read now is one branch in the client and one row in the
docs. The cost of adding it after every bay has a file is a migration.

## 5. What this does not change

- `machinenumber` and its GE-Enforce gating. Untouched in all three phases.
- A part marker still files `partof` the operation from `machinenumber`. The
  device identity says WHICH marker the PC controls, not which operation that
  marker belongs to.
- Minting. It stays as the last resort for a bay that names nothing, because a
  device nobody declared is still better recorded than not recorded. Anything
  minted should be treated as a placeholder to be reconciled.

## 6. Before phase 2: find what is already duplicated

Phase 1 stops NEW duplicates. It does not merge the ones a PC swap has already
created. Before imaging starts writing files, run a read-only query for device
assets whose controlling PC no longer exists, or whose asset number carries a
hostname that is not a current PC. That list is the reconciliation backlog, and
it is much easier to read before the fleet starts reporting new identities over
the top of it.

## 7. Rollback

Each phase is independently reversible because nothing is removed until the
phase after it proves the replacement:

- Phase 1: stop sending `deviceid` and every previous fallback still runs.
- Phase 2: stop writing `asset-id.txt` and bays fall back to what they used
  before.
- Phase 3: stop writing the registry value and bays fall back to the file.

The only irreversible step is deleting a fallback branch, which is deliberately
outside all three phases.