Add an update command that reads, diffs, and writes

[oveddan]

Read the controller, work out what differs, write only that.

The existing export/plan/apply flow exists so a plan can be reviewed before applying. Worth having, but it is not what most changes need — and it fails the README's own motivating example:

$ mft-config plan --snapshot snap.json --set bank.1.encoder.1.colors.active=green ...
mft-config: bank.1.encoder.1.colors.active is already 43

Asking for the top row to be green aborts if any one of those knobs already is. That is correct for plan, where the contract is "the state I described is the state I found". It is wrong for an update.

$ mft-config update --set bank.1.encoder.1.colors.active=green ... (4 knobs)
unchanged  bank.1.encoder.1.colors.active is already 43
unchanged  bank.1.encoder.2.colors.active is already 43
change     bank.1.encoder.3.colors.active: 43 -> 1
change     bank.1.encoder.4.colors.active: 43 -> 1

2 change(s) not written. Re-run with --yes to apply.

Verified against real hardware.

Why this is not behind the #14 gate

No plan file changes hands, so there is nothing to forge and nothing to replay — the entire class of defect in #14 comes from serialising a plan, handing it to someone else, and reading it back. update therefore needs neither the journal nor the single-use machinery, keeps no hidden state, and writes a backup file you name. 0d, the cwd-relative state root that apply is gated on, does not apply to it.

It still gets every device-side guard: fresh export, precondition check on each value, firmware eligibility recomputed from the device, frames derived and verified, and full read-back.

Notes

• planUpdate rejects two --sets for one field rather than picking a winner
• it delegates to createPatchPlan once no-ops are filtered, so both paths build frames through identical code
• an update where everything is already set succeeds having done nothing

🤖 Generated with Claude Code

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 95449ff177

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Keep the journal separate from the requested backup

When --backup names <directory>/mft-updates.ndjson, saveBackup first writes the JSON snapshot there and then applyPatchPlan appends journal records to the same path. The command reports this file as the backup, but it is no longer valid JSON and cannot be used for restoration. Since the CLI permits any backup filename and does not reserve this name, reject this collision or store the journal at a path that cannot overlap the requested backup.

Useful? React with 👍 / 👎.