49 lines
2.6 KiB
Markdown
49 lines
2.6 KiB
Markdown
---
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status: resolved
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opened: 2026-09-02
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located-in: [mesh-host internal/apply (file create-once), mesh-host examples]
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fixed-by: ADR 0087; mesh-host #16 (a file resource may say create-once; kept, never corrected); proven by the apply tests and the vault bed
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amended-design: 03-DESIGN/01-to-be/18-building-a-module.md
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---
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# 035 — Reconciling a seed file wipes what grew in it
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## The symptom, as observed
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Found by review of the catalogue examples (2026-09-02), not by an outage — the outage is the
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part the design permits to be silent.
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The cache module declares its access-control file as an ordinary file resource with fixed,
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empty content. The program that consumes the file requires it to exist at startup, which is
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why the manifest declares it at all. But the same file is the one the provisioner writes
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consumer users into, and the one the running program persists ACL changes back to.
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A declaration is complete for what the host owns, and the host reconciles what is declared
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([ADR 0010](../../02-DECISIONS/0010-delivery.md)).
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So every apply that revisits this resource restores the declared content — empty — behind the
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running program. Every consumer credential granted since the last apply is removed, the apply
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reports success, and nothing anywhere says a grant vanished.
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## Why it matters beyond the instance
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The manifest needed *the file to exist before first start*, and the only vocabulary available
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was *the file has this content, forever*. Those are different intentions, and the gap between
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them is generic: any resource that a module seeds and something else then legitimately mutates
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— an ACL file, a bootstrap configuration a program rewrites, an htpasswd a provisioner appends
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to — has the same two owners and the same silent loss on reconcile.
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It is also the mirror image of the boundary ADR 0010 draws so carefully on the *removal* side:
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the host never removes what it did not create, but it happily overwrites what it *did* create,
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even when what grew inside since is somebody else's work the mesh asked for.
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## Open questions
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- Is the missing thing a create-once file semantic ("present with this content if absent,
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untouched otherwise"), or is the real fault that two owners share one file — and the
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provisioner, not the declaration, should own it entirely, with first-start ordering solved
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some other way?
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- ADR 0010 treats every added resource type as a security artefact. Does a create-once
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semantic widen what a compromised control plane can express, or narrow it?
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- Are there other seeded-then-mutated files already in the catalogue that this failure is
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waiting inside?
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