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ADR 0088: Host slot, attention region and deck cell - taxonomy (do not mix)

Status: Proposed
Date: 2026-04-22

ADR Role
0017 zone Mfd vs pages MfdShellView
0021 PFD/MFD anchors, geography vs telemetry
0047 CockpitInstrumentDescriptor, slot_id
0050 [instrument_routing], pfd_primary / mfd_primary
0063 instrument deck, InstrumentDeckDescriptor, SemanticAnchorId
0068 row payload vs projection vs slot
0073 PFD Candidate Directory
## Summary
  • Taxonomy host slot / region / deck cell - do not mix levels.
  • Contact with 0068.

Summary: in discussions slot was called both the entire PFD column and small rectangle in the instrument grid. This ADR captures the dilution of levels: what is a host slot in the host wire, what is a region/attention anchor, what is an instrument deck cell - and what not to mix. A multi-tool implementation on a PFD (surface deck composer) is not required to change the meaning of CockpitSlotIds.Pfd without separate agreement (see §4).

1. Context: where the confusion comes from

  1. In the code CockpitSlotIds.Pfd / Mfd are identifiers for MainWindowHostSurfaceCompositor: no more than one CockpitInstrumentDescriptor per each such identifier is included in the frame; geographically this is the entire visible PFD (or MFD) column in the DockedGrid, not the "single tile" within it.
  2. In product speech, PFD is zone of primary attention (whole column, separate P+M window, etc.).
  3. Instrument deck [0063] introduces a named composition "multiple entities in one anchor" with SemanticAnchorId = for example pfd - the same word as slot_id, but different level of abstraction (InstrumentDeckDescriptor vs host frame).
  4. In 0068 table row/lane and cell type are already separated; All that remains is to explicitly associate this with the host slot [0047].

Without fixed names, the question again arises: “Is a slot the entire PFD or a cell in the deck?”

2. Solution: canonical levels

Below are recommended terms in documentation, ADR, review; in the code, the identifiers (CockpitSlotIds, TOML fields) do not have to match these Russian/English names verbatim, but the meaning** must be mapped.

Rough “staircase” from top to bottom (different branches): window topology / presentation (0017) → attention region (PFD, MFD) → shell page (MfdShellPage, §2.0) - for the secondary circuit; in parallel on the PFD side - host slot (§2.1) and then deck / internal blocks of the device. Page sits above the route “what is the cabin instrument_id in pfd”, otherwise chat would be confused with instrument.

2.0. Shell Page (Page, MfdShellPage)

  • Definition: navigation inside MfdShellView - which entire mode occupies the column of the secondary outline: Chat, Terminal, Solution Explorer, Build, ... (Models/MfdShellPage.cs, command set_mfd_shell_page in 0030).
  • Level: above §2.1–2.4: this is not CockpitSlotIds, not CockpitInstrumentDescriptor, not instrument deck cell. Changing the page is orthogonal to selecting a PFD device in the host frame.
  • Connection with 0017: Mfd focus area (column/window) ≠ page; chat is page, not “another area” next to the PFD.
  • PFD branch: in v1 there is no analog MfdShellPage for the PFD column as a switchable set of unrelated UIs: there is basically one mounted cockpit device (§2.1), its internal mosaic is §2.4. For Pfd, call navigation layout, not page stack: contract IPfdLayout + PfdLayouts in Models/Shell/. For Mfd - IShellPage / IMfdShellPage + MfdShellPageDescriptor (the same MfdShellPage in VM).

2.1. Host slot (host slot, slot_id in CockpitInstrumentDescriptor)

  • Definition: unit of instrument routing in the host frame of the main/sub window: where the composer places the relevant instrument_id to be displayed in a given geometric column zone.
  • Today (v1): one instrument_id per host slot; example: CockpitSlotIds.Pfd + CockpitStandardInstrumentIds.WorkspaceNavigationMap.
  • Map: MainWindowHostSurfaceCompositor.BuildInstruments → list CockpitInstrumentDescriptor(InstrumentId, SlotId).
  • Not to be confused with: small glyph, row in WH table, sub-slot inside Avalonia markup of one UserControl.

Invariant v1: host slot does not split into multiple slot_ids in the same frame model unless [0047] is expanded explicitly (see §4).

2.2. Region/attention anchor (PFD, MFD, …)

  • Definition: semantic zone of the cockpit by [0021] - why this part of the screen (primary scan, secondary contour, ...).
  • Relation to host slot: for primary/docked columns geography “PFD column” coincides with host slot pfd as screen area; The anchor explains the role of the zone, the host slot is the attachment point in the frame DTO and the MCP narrative of “mount tool X in Y”.

2.3. Instrument deck and deck cell (deck cell)

  • Definition [0063]: named composition: an ordered set of cells (grid, stack, stripe) under SemanticAnchorId.
  • Deck cell: one position in the layout: stable cell_id (like EnvironmentReadinessInstrumentDeck.OrderedCellIds, IdeHealthInstrumentDeck.OrderedSegmentIds for the channel IDE Health - analogue in role).
  • Critical: the deck cell is not a CockpitSlotIds in the current contract [0047] unless an explicit mapping "cell → host slot / nested route" is entered.
  • Purpose: several indicators/tools within the geography of one PFD region (for product decision) - through another layer: either a composite UserControl (internal layout = not a deck in the host sense), or a future deck host / PFD surface deck compositor (see §3).

2.4. The entire device and internal units (device cells)

Orthogonal to §2.3: one instrument_id in the host slot (for example, an intent map in Pfd) itself can be composite - the pilot perceives one instrument, and inside there are several blocks (cells), which contain specific indicators, subgraphs, legend, chrome, signatures (0064 - types of primitives).

  • Internal cell / block - unit of layout inside of one cabin instrument; stable id and composition policy are set by the composer of this device (for the mini-map - intent map pipeline, see 0055, 0056), not to be confused with cell_id instrument deck at the region level (§2.3).
  • Meaning for UX: “device = composition of blocks” - then, for example, a graph and a legend for it are two such blocks with explicit layout (reserve for a legend, independent scaling, etc. for the product), and not one indistinguishable mess.
  • Implementation (PFD v1 map, Intent Map product): graph/legend partitioning - CodeNavigationMapInstrumentBlockCompositor + CodeNavigationMapInstrumentBlockDescriptor / CodeNavigationMapInstrumentBlockIds in Services/CodeNavigation/ (stable ids code_navigation.pfd_instrument.block.*); alternative composer with id code_navigation.workspace_instrument.block.* - CodeNavigationMapWorkspaceInstrumentBlockCompositor in Services/Navigation/. The result of the pipeline is CodeNavigationMapCompositionResult.CodeNavigationMapInstrumentBlocks (after CodeNavigationMapLayoutStage in CodeNavigationMapCompositor). The drawing is uniform (CodeNavigationMapSceneDrawing), rectangles are consistent with LegendColumnLeft / LegendBlockTopY.

Invariant of terms: deck on PFD = deck of several (cockpit) instruments in the region; block = part of one device. When talking about “cell”, specify: deck cell (region) vs internal cell of the device.

3. Direction of implementation (without fixing a deadline)

  1. Toolbox Composer on one PFD geometry: takes InstrumentDeckDescriptor (or PFD-specific variant) and projects instrument_id to cells; An external host frame can still contain one descriptor on pfd with instrument_id = deck host, or - when extending the model - otherwise; selecting a separate iteration after the prototype.
  2. CDS / MCP / snapshot: what is considered an “atom” in a frame (one host instrument vs N internal ones) - contract boundary; update [0008] / cds-contract together with implementation, do not degrade "one instrument_id in pfd" undetectably.

4. Rule of distinction: “what is called a slot in a conversation”

Question Canonical answer (this ADR)
“Is the slot the entire PFD?” Host slot pfd in the sense of [0047] / host frame - yes, this is a route to the column (one selected tool for this area in v1).
“A slot is a small cell in the instrument grid?” No for CockpitSlotIds; name cell deck / cell_id.
"Is SemanticAnchorId = pfd in InstrumentDeckDescriptor the same as slot_id?** Same attention anchor/region, not a duplicate of a separate host slot in the DTO, until the deck is raised into the frame as a separate layer; avoid "two pfd in one frame" in speech without qualification.

5. Consequences

  • Documentation, new ADRs, review: use host slot vs deck cell vs PFD region according to table §4.
  • 0073 (PFD catalogue) and 0063 remain: this ADR clarifies the terms, does not replace them.
  • Code: immediate change of CockpitSlotIds names not required; when a PFD multi-instrument appears - either an internal deck without a new slot_id, or an explicit extension 0047 + entry in the MCP changelog.

6. Rejected alternatives

  • Read "slot" micro-cell only - breaks the current MCP language/"mount in pfd" and [0047] without migration.
  • Rename CockpitSlotIds.Pfd to PfdColumn and enter PfdCell_0... - possible in the future, but high price; until consensus we use §2–4.
  • Mix WH line and host slot - already covered in [0068]; we don't repeat.

7. Open questions (do not block Proposed)

  • Exact wire: one instrument_id “PFD deck host” vs an array of descriptors in MainWindowHostSurfaceFrame - based on PoC of the composer.
  • Stable cell_id for PFD-desk vs TOML presets - evolution of [0050] / [0063 § deck in presets].

Brief glossary (for copy-paste)

Term Meaning
Page MfdShellPage - what content of the secondary circuit in the Mfd column (chat, terminal, ...); above host slot [0047]; 0017.
Host slot slot_id in CockpitInstrumentDescriptor / CockpitSlotIds - mount point in host frame; v1: entire PFD (or MFD) column, one selected instrument_id.
Region / Attention Anchor PFD, MFD - cockpit area [0021]; Geography is often 1:1 with host slot, semantics is “zone role”.
Instrument deck Named composition within anchor; SemanticAnchorId = region.
Deck cell (cell) Position in the regional deck; not CockpitSlotIds in v1.
Block / internal cell of the device Unit within one instrument_id (graph, legend, indicator bar); composer of the device, not the host deck.