The Principia Machina/Diagrams/09 Lock and petition queue

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The specification Contents: parts, tables, diagrams TPS 0.5.0 (declared 2026-10-03, revision 8; machine-optimized text) Decisions (the foundations record, one line each)

Structural diagram 9 of 13. Part of the TPM hub.

• KIND: process
• LANGUAGE: Mermaid
• GENERATED FROM: per-UWC lock page state; TPS 5.7, 5.8.5
• STATUS: hand-authored at TPS 0.1.0; checked against TPS 0.3.0 on 2026-09-28: owed a redraw (the heartbeat is drawn as a lock-page edit; not drawn: the NO-PROGRESS rule, the expiry steps and AGENT STOP, 5.7.8-5.7.10); superseded by TPX at its first build
• SOURCE SHA-256: 81ec061ed163dedd97c5edebe4f77e6bb309b7ca557883142929c68c7f206877

Rendered live from the source, which is the text equivalent and is shown under the drawing. The key to the shapes is in the panel.

Source (the text equivalent; Mermaid)

%% 09 Lock and petition queue. process/Mermaid sequence. Generated from: per-UWC lock page state; TPS 5.7, 5.8.5.
sequenceDiagram
  participant L as Lead (holder)
  participant K as Lock page
  participant X as TPX
  participant C as Coworker (queue head)
  L->>K: base-revision edit: holder, grant plus 1, grant time, expiry (5.7.2)
  L->>K: heartbeat every few hours, never past 24 h from grant (5.7.3)
  L->>X: push carrying the grant number (5.9.8)
  X-->>L: fencing check: grant not stale, holder is pusher, badge written last (5.10.1)
  L->>K: release, valid only after the push (5.7.5)
  C->>K: acquire as queue head within the ACQUISITION WINDOW (5.7.4)
  Note over K,X: out-of-order or pre-expiry acquisition refused by the save hook (5.7.1)
  Note over C,K: if the head is silent past the window, the next waiter may acquire (5.8.5)

Text equivalent

The lead acquires the lock by a base-revision edit writing holder, grant, grant time and expiry (5.7.2), extends it by heartbeats never past 24 hours and only while it has pushed or returned within the NO-PROGRESS LIMIT (5.7.3, 5.7.8), pushes with the grant number under the fencing check with the badge written last (5.9.8, 5.10.1), and releases only after that push (5.7.5). Heartbeats are kept in the table of TPX, the controller, not written to the lock page as the drawing shows; the lock page and the badge record the expiry at acquisition, at release and at each EXPIRY STEP (5.7.9), and the operator's AGENT STOP stops the lock clocks (5.7.10). The queue head acquires within the ACQUISITION WINDOW, else the next waiter may (5.7.4, 5.8.5); the save hook refuses any out-of-order or pre-expiry acquisition (5.7.1).