docs(flomni): add design plan for Brother P-touch label printer integration

Feasibility/design session output: print account+date labels on
sample-tray unload via P-touch Template mode, as a shared OMNY_shared
utility rather than an ophyd device.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UGC1TfxZJvJHs6Qz1V8w1h

docs/developer/ptouch_label_printer_plan.md

@@ -0,0 +1,166 @@
+# Brother P-touch PT-P950NW label printing for BEC: design plan
+
+> **Status: proposal, not yet implemented.** This document captures the plan
+> from an initial feasibility/design session so it isn't lost; it should be
+> updated (or removed / folded into an architecture note) once the feature is
+> actually built.
+
+## Context
+
+When a measured sample is unloaded from the flomni sample tray, the only record
+of "who owns it / when it was measured" today is digital (tray-slot metadata
+in `dev.flomni_samples`, plus the OMNY sample database via `TomoIDManager`).
+There is no physical label on the actual sample holder, so a user picking it
+up later has no way to tell at a glance whose sample it is or when it was
+run. The goal of this feature is to print a small paper label (account +
+date, on TZ tape) at the moment a measured sample is stowed back in the tray,
+so it can be stuck straight onto the sample holder.
+
+This is explicitly **not** an experiment hardware component (no motion, no
+staging, nothing that needs to be part of a scan) — it's a side-effect
+utility, similar in spirit to the existing `TomoIDManager` (HTTP registration
+call) and `HttpUploader` (webpage push) helpers, which are plain Python
+classes invoked from the flomni/lamni plugin code at well-defined workflow
+points, not ophyd devices.
+
+**Decisions already made:**
+- Protocol: **P-touch Template mode** (Brother's official, documented
+  command protocol) rather than the raster/reverse-engineered protocol used
+  by third-party libraries like `rasterprynt`. This avoids needing an image
+  library (Pillow) client-side and avoids depending on an undocumented
+  protocol that could break on a firmware update — fits the goal of
+  minimizing external packages.
+- Scope: build as a **shared utility** in
+  `bec_ipython_client/plugins/OMNY_shared/`, so lamni/omny can adopt it later
+  without duplicating printer/network code — mirrors where `TomoIDManager`
+  and `HttpUploader` already live.
+- Trigger: **both**. Automatic prompt-then-print on sample unmount in flomni,
+  plus a manual/standalone command for on-demand (re-)printing.
+
+## How P-touch Template mode works (research summary)
+
+- The PT-P950NW supports raw network printing on **TCP port 9100** (listed
+  in its spec sheet alongside LPR/IPP/mDNS etc.), the same "JetDirect-style"
+  raw port most network printers use — no CUPS/driver install needed.
+- "P-touch Template" is a printer-side mode built for exactly this use case
+  (the manual explicitly lists "data from a scale, testing machine,
+  controller, or PLC" as the target): you design a label layout **once** in
+  Brother's Windows-only **P-touch Editor** (place named text objects, e.g.
+  `ACCOUNT`, `DATE`), transfer that template onto the printer's internal
+  memory (via Editor's Transfer Manager over USB or network), and from then
+  on printing is just: connect to the printer, send a short **ESC i X**
+  command sequence selecting the template number and supplying the text for
+  each named field, then a print-start command.
+- The command set is documented in Brother's "P-touch Template Command
+  Reference" (per-printer-family PDF from Brother's support site — confirm
+  the PT-P900W/P950NW-specific revision before implementing, since control
+  codes can differ slightly between printer families/firmware generations).
+- No actively-maintained Python package implements this specific protocol
+  (unlike raster printing, which has `rasterprynt`/`brother_ql`-style
+  libraries). That's fine here: the runtime protocol is just building a byte
+  string and pushing it over a `socket` — stdlib only, no new dependency.
+
+## Implementation plan
+
+### 1. New shared module: `PTouchLabelPrinter`
+
+File: `csaxs_bec/bec_ipython_client/plugins/OMNY_shared/ptouch_printer.py`
+(new file, alongside `omny_general_tools.py`/`web_common.py`).
+
+```python
+class PTouchLabelPrinter:
+    """Prints a label on a Brother PT-P950NW via P-touch Template mode."""
+
+    DEFAULT_PORT = 9100
+
+    def __init__(self, host: str, template_number: int = 1, port: int = DEFAULT_PORT, timeout: float = 3.0):
+        ...
+
+    def print_label(self, fields: dict[str, str], copies: int = 1) -> bool:
+        """Build the P-touch Template command for `fields` and send it.
+
+        Returns True on success, False on any network/printer error --
+        never raises, matching TomoIDManager's fail-soft convention so a
+        printer being offline can never block a sample transfer.
+        """
+        ...
+```
+
+- Builds the ESC-prefixed command sequence (select template mode, select
+  template number, set each named field's text, set copy count, print
+  command) as pure bytes, opens a short-lived `socket.create_connection((host,
+  port), timeout=timeout)`, sends, closes.
+- Wrap all I/O in `try/except`, `logger.warning(...)` on failure, return
+  `False` — same fail-soft style as `TomoIDManager.register()`
+  (`omny_general_tools.py:396-`) and `HttpUploader` (`web_common.py:48-114`).
+- Printer host/IP and template number are constructor args (not hardcoded
+  constants), passed in from each plugin's config — check how other
+  beamline-specific endpoints are configured in this repo (e.g. is there a
+  per-instrument config file, or are they class constants like
+  `TomoIDManager.OMNY_URL`?) and follow that convention when wiring it up.
+
+### 2. Wire into flomni
+
+File: `csaxs_bec/bec_ipython_client/plugins/flomni/flomni.py`
+
+- Instantiate once in `__init__`, next to `self.OMNYTools = OMNYTools(...)`
+  (line ~1654) and `self.tomo_id_manager = TomoIDManager()`:
+  `self.label_printer = PTouchLabelPrinter(host=<printer-ip>, ...)`.
+- **Automatic path**: in the unmount branch of `ftransfer_sample_change`
+  (the `new_sample_position == -1` case, `flomni.py:867-906`) or in
+  `ftransfer_get_sample` (`flomni.py:734`, name/owner already unpacked at
+  line 786-787 as `name, owner = unpack_desc(signal_name.get())`), after the
+  stow completes: ask `self.OMNYTools.yesno("Print a label for this sample?",
+  "y")` (same helper already used elsewhere, e.g. `flomni.py:2507`) and on
+  `True` call `self.label_printer.print_label({"ACCOUNT": owner, "DATE":
+  str(datetime.date.today())})`.
+- **Manual path**: add a small method, e.g. `fprint_sample_label(position:
+  int)`, that reads name/owner via the same `unpack_desc(...)` pattern as
+  `sample_get_name` (`flomni.py:853`) and calls `label_printer.print_label`
+  directly — usable standalone for reprints, without going through a
+  transfer.
+
+### 3. Open items to resolve before/during implementation
+
+- **No date is currently stored per sample slot** — `pack_desc`/`unpack_desc`
+  (`devices/omny/sample_desc_codec.py:19,40`) only carry `(name, owner)`, no
+  timestamp. Using `datetime.date.today()` at unmount time is a reasonable
+  v1 approximation (unmount typically happens same-day as the scan), but if
+  an exact measurement date is wanted later, the DESC codec would need a
+  third field.
+- **Confirm the exact model-specific command reference.** Brother publishes
+  a separate "P-touch Template Command Reference" per printer family;
+  download the PT-P900W/P950NW-specific PDF from Brother's support site
+  before writing the byte-level command builder.
+- **Template design is a one-time, Windows-only step** (P-touch Editor +
+  Transfer Manager) — not scriptable from the Linux beamline control host.
+  Worth doing once per label layout/TZ tape width; layout changes require
+  redoing this step.
+- **Network reachability**: confirm the printer's IP is reachable from
+  wherever `bec_ipython_client` runs (same VLAN/firewall rules as other
+  network endpoints it already calls, e.g. the OMNY/tomo-ID server) and
+  assign it a static/reserved IP.
+- Extend to lamni/omny by instantiating `PTouchLabelPrinter` in those
+  plugins too once flomni is validated — no code changes needed to the
+  shared module itself.
+
+## Verification
+
+1. **Bench test the printer/template alone**: install the PT-P950NW on the
+   beamline network with a fixed IP, design the label template once in
+   P-touch Editor (fields `ACCOUNT`/`DATE`, chosen TZ tape width), load it
+   via Transfer Manager, and print a manual test label from the desktop app
+   to confirm the template renders as expected.
+2. **Bench test the protocol module standalone**: write
+   `PTouchLabelPrinter`, then from a scratch script call
+   `print_label({"ACCOUNT": "e12345", "DATE": "2026-07-31"})` against the
+   real printer IP and confirm a correct physical label comes out (check
+   encoding, field placement, tape length/cut).
+3. **Integration test in flomni**: in a real or simulated
+   `bec_ipython_client` session, run `ftransfer_sample_change(-1)` (or
+   `ftransfer_get_sample`) end-to-end, confirm the yes/no prompt appears,
+   confirm printing on "y", confirm declining or a deliberately-unreachable
+   printer IP does **not** raise or block the sample transfer (only logs a
+   warning).
+4. Test the manual `fprint_sample_label(position)` command independently of
+   any transfer, for reprints.