docs/ befuellt - Stack-Hintergrund fuer vier Themen, Pflegeklausel in AGENTS.md ergaenzt (4.3.1, #45)

Files changed:
- AGENTS.md
- CHANGES.md
- VERSION
- docs/ownership-and-templates.md
- docs/pipeline-rationale.md
- docs/version-model.md
- docs/why-gates-are-code.md

docs/ownership-and-templates.md

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+# Ownership and Templates
+
+Chemenu ships two kinds of files side by side, and at a glance they look the same: both are
+plain markdown, both sit in the repo root or under `kb/`, both get read at session start. But a
+stack upgrade treats them completely differently. Some - [AGENTS.md](../AGENTS.md),
+[kb/CONTRACT.md](../kb/CONTRACT.md), the per-stage contracts - are identical in every instance
+that runs this stack and can simply be overwritten by the next release. Others - `USER.md`,
+`SOUL.md`, `kb/CONVENTIONS.md`, `ENVIRONMENT.md` - describe one particular instance, and
+overwriting them would silently erase a choice someone made on purpose.
+
+## Two different kinds of truth
+
+The stack-owned files describe how the tool works. `kb/CONTRACT.md` opens by saying it holds
+what `tools/wikitool` enforces or what follows mechanically from how it operates - see
+[kb/CONTRACT.md](../kb/CONTRACT.md), lines 10-13. That kind of statement doesn't vary by
+instance: the compiler behaves the same way regardless of who is running it, so the sentence
+describing that behavior can be copied byte-for-byte into every checkout without becoming
+wrong anywhere.
+
+The instance-owned files describe a choice: which language pages are written in, what tone the
+agent takes, who the operator is, which git remote is authoritative, which MCP servers are
+reachable. None of that follows from the tool's mechanics - two instances of the identical
+stack can answer all of these differently and both be correct. [AGENTS.md § Personalization](../AGENTS.md#personalization)
+frames the split the same way for `kb/CONTRACT.md` versus `kb/CONVENTIONS.md`: "the split is by
+who may change the sentence, not by what it is about." A rule about page structure could in
+principle have been written per-instance too, but then every instance answering "not German" to
+setup would be hand-editing a file the stack also ships, and the next `dist export` merge would
+hand the instance's own file back to it, discarding the customization.
+
+## Why silent overwrite is the failure being designed against
+
+A stack update is meant to be a routine, low-risk operation: pull the latest release, get
+whatever fixes and features shipped since the last one. That only stays low-risk if the update
+knows which files it's allowed to touch. If `USER.md` or `kb/CONVENTIONS.md` were treated the
+same as `AGENTS.md` - shipped and periodically re-copied - an upgrade would quietly replace a
+description of *this* operator, in *this* language, with whatever placeholder or default the
+stack maintainers wrote. The damage wouldn't be loud: nothing crashes, the files still parse,
+the agent just starts acting on the wrong premises until someone notices the voice or the
+language changed.
+
+Keeping the boundary at the file level, rather than trying to merge changes within a shared
+file, means an upgrade never has to guess which lines are "stack" and which are "instance" -
+the file itself already answers that.
+
+## Why a `.template`, not just an absent file
+
+The mechanism for instance-owned content is a `.template` file the distribution ships instead
+of the real one - `USER.md.template`, `SOUL.md.template`, `kb/CONVENTIONS.md.template`,
+`ENVIRONMENT.md.template`. An alternative would have been to ship nothing at all and let a
+brand-new instance start from a blank page. The template exists because a blank page doesn't
+tell [instructions/setup-instance.md](../instructions/setup-instance.md) what shape the answer
+should take, and it gives nothing for a validator to check afterward.
+
+A template carries a placeholder value - a sentinel - in the fields that need a real answer.
+Setup interviews the operator and replaces the sentinel with what they actually said. That
+gives `doctor` a mechanical way to tell "personalized" from "not yet": a file that still
+contains the sentinel hasn't been through setup, regardless of whether the file exists. That's
+also why `ENVIRONMENT.md` only warrants a WARN rather than a FAIL when absent - see
+[AGENTS.md § Environment](../AGENTS.md#environment) - while a missing or unfilled
+`USER.md`/`SOUL.md`/`kb/CONVENTIONS.md` is a harder failure: `ENVIRONMENT.md` describes one
+checkout among possibly several and is gitignored for that reason, so its absence is a normal
+state rather than a sign setup was skipped.
+
+## The consequence in practice
+
+Running a stack upgrade against an existing instance boils down to: overwrite the verbatim
+files, leave the `.template`-sourced files alone. The verbatim files are safe to replace
+wholesale because they were never instance-specific to begin with - identical content going
+back in changes nothing an instance actually decided. The template-sourced files were filled in
+once, by a person, for a reason, and nothing about a newer release of the stack's mechanics
+gives it standing to override that.