docs(agents): drop the fact-placement convention from AGENTS.md (#121)

* docs(agents): drop the fact-placement convention from AGENTS.md

Where a fact goes, its admission check and the ADR convention all go; doc
placement is a domain-modeling convention. The INVARIANT: docstring shape stays.

* docs(agents): drop inline ADR citations from AGENTS.md

The remaining docs/adr/ references were citations inside architecture prose,
or an index of them. The prose stays; the pointers go.

Author: lesnik512

AGENTS.md

@@ -25,9 +25,6 @@ re-exported as-is. Three protocol seams — client ↔ middleware chain, client
 httpware ↔ optional extras — are defined in `CONTEXT.md` and named **A**, **B** and **C** in the
 module docstrings that implement them. Never cross a seam except through its protocol.
 
-Behavior detail has no prose home — it lives in the code and its `INVARIANT:`-marked tests. Before
-writing prose about a capability, run the admission check in **Where a fact goes** below.
-
 ### Key files
 
 Every module under `src/httpware/` is named for what it does; read it. What a single-file read will
@@ -68,38 +65,12 @@ parallelism: they run under the GIL for coverage, but the proof comes from the f
 
 ## Workflow
 
-Two things outlive the PR, and there are exactly two places to put them: an alternative
-**rejected** with reasoning becomes an ADR in [`docs/adr/`](docs/adr/) (`NNNN-slug.md`,
-sequential), and real work **not scheduled** becomes a GitHub issue. There is no third state, and
-no separate truth-home directory — a behaviour change is reviewed with the diff, not promoted to a
-page.
-
-### Where a fact goes
-
-Four homes, one owner each:
-
-| Home | Holds |
-|---|---|
-| `src/httpware/` | anything readable from the module — the default |
-| a named test | an **invariant**: must stay true, and a change could silently break it |
-| `docs/adr/` | a rejected alternative, with the reasoning that would otherwise be re-litigated |
-| `docs/` | anything a user needs |
-
-Before writing a line anywhere:
-
-> Can an agent get this by reading `src/httpware/`? → **don't write it.**
-> Would a wrong change here fail a test? → it belongs **in the test**, not in prose.
-> Does a user need it? → **`docs/`**.
-> Otherwise it does not get written.
-
-**Prose about mechanism has no home. There is no file to add a paragraph to.** This file included:
-it is always loaded, so a line that restates a docstring, a justfile comment, or `pyproject.toml`
-costs every turn and rots in two places at once.
+Real work **not scheduled** becomes a GitHub issue.
 
 An invariant is a test whose name is the claim, with a docstring opening `INVARIANT:` and a second
 paragraph naming **what breaks it** — design rationale, not a report of what this one test catches;
-a sibling test may be the one that trips. Both ADRs and `INVARIANT:` docstrings ratchet: nothing
-prunes a record once its call is settled. Keeping them lean is a standing habit.
+a sibling test may be the one that trips. Nothing enforces that docstring shape; it is read at
+review time.
 
 ## Code Style
 
@@ -111,7 +82,7 @@ prunes a record once its call is settled. Keeping them lean is a standing habit.
   `ty`, which silently accepts the latter without checking the rule
 - Docstrings: public API documents the contract; internal helpers get a one-line contract, plus at
   most 1–2 lines for a genuinely non-obvious constraint. Never narrate implementation or justify
-  code to a reviewer — cross-file rationale lives in an `INVARIANT:` test docstring or an ADR
+  code to a reviewer — cross-file rationale lives in an `INVARIANT:` test docstring
 
 ## Agent skills