docs: restore the two backlog paths RD-19's target of 0 removed

RD-18 established that a ticket reference inside a path to a document that
still exists is a pointer, not provenance, and exempted one. RD-19 did not
re-run that check against `backend/`, and asserted a target of 0. Two such
paths existed, so the agent described the two documents in prose instead. The
path no longer resolves and the reader must search.

Restore both paths, correct the ticket's decision 1 and acceptance target to
2, and record the miss as the eighth in the README's list.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/README.md

@@ -15,7 +15,7 @@ status codes and error envelope are production-shaped.
 covers it, see `docker-compose.yml`) does **not** lose data. Delete the file to
 reset demo data back to empty, the same state a fresh clone starts from. This is
 a deliberate, right-sized choice for a POC (SQLite, no external DB service) — see
-the durable-persistence design note in `docs/project/backlog/`.
+`docs/project/backlog/WP-22-durable-persistence.md`.
 
 ## Run
 

backend/src/BigRegister.Api/Domain/Letters/LetterHtml.cs

@@ -151,9 +151,8 @@ public static class LetterHtml
   private static string EncLines(string s) => Enc(s).Replace("\n", "<br>");
 
   // Walks up from the running assembly's own directory (NOT the process cwd, which
-  // varies by how `dotnet run`/docker/tests invoke it — see the letter-preview-html design
+  // varies by how `dotnet run`/docker/tests invoke it — see
-  // note in docs/project/backlog/) until
+  // docs/project/backlog/WP-25-letter-preview-html.md) until it finds `public/letter.css`. docker-compose.yml bind-mounts `./public` under the
-  // it finds `public/letter.css`. docker-compose.yml bind-mounts `./public` under the
   // api container's `/src` for exactly this walk to resolve there too.
   private static string FindLetterCss()
   {

docs/project/readable-codebase/RD-19-ticket-refs-backend.md

@@ -25,10 +25,22 @@ Strip the reference, keep the sentence. No behaviour changes.
 
 ## Decisions (pre-made, don't relitigate)
 
-1. **Nothing in `backend/` is exempt. Strip all 370.** Unlike the front end, no backend file
+1. **Strip all 370 except two.** No backend file disables a check by naming the ticket that
-   disables a check by naming the ticket that removes it — verified against
+   removes it — verified against `pragma warning disable`, `Skip =`, `NoWarn` and
-   `pragma warning disable`, `Skip =`, `NoWarn` and `SuppressMessage`, none of which carries a
+   `SuppressMessage`, none of which carries a reference. Keep all 40 `ADR-000x` references; that
-   reference. Keep all 40 `ADR-000x` references; that count must not move.
+   count must not move.
+
+   **Corrected after the ticket ran.** The original text said "nothing is exempt", and it was
+   wrong. Two references are part of a path to a document that still exists:
+
+   | Site                               | Reference                                           |
+   | ---------------------------------- | --------------------------------------------------- |
+   | `backend/README.md:18`             | `docs/project/backlog/WP-22-durable-persistence.md` |
+   | `Domain/Letters/LetterHtml.cs:153` | `docs/project/backlog/WP-25-letter-preview-html.md` |
+
+   RD-18 exempted this same class of reference (`a11y.mdx:68`). A path that resolves is a
+   pointer, not provenance. Stripping the number breaks the path, and describing the file in
+   prose instead makes the reader search for it.
 
 2. **`public/letter.css` and `LetterHtml.golden.html` change together, or the build goes red.**
    `LetterHtml.cs:161` finds `public/letter.css` at run time and **inlines it** into the
@@ -96,7 +108,14 @@ Measured against the tree before handover. `git grep -o … | wc -l` counts **oc
 `git grep -c` counts lines and would give a different, wrong number.
 
 ```bash
-git grep -oE "\b(WP|RB)-[0-9]+" -- backend public/letter.css | wc -l   # is 373 -> MUST be 0
+git grep -oE "\b(WP|RB)-[0-9]+" -- backend public/letter.css | wc -l   # is 373 -> MUST be 2
+```
+
+The two survivors are the document paths in decision 1:
+
+```bash
+git grep -oE "\b(WP|RB)-[0-9]+" -- backend/README.md \
+  backend/src/BigRegister.Api/Domain/Letters/LetterHtml.cs | wc -l    # MUST be 2
 ```
 
 The ADR references survive, and the sweep leaves no damaged prose:

docs/project/readable-codebase/README.md

@@ -198,6 +198,15 @@ Three rules when you write a ticket file, because the agent reads its ticket and
      on word boundaries**: `git grep -w machineRemoteData` and
      `git grep -nE "(^|[^a-zA-Z])LoadLifecycle\b"`.
 
+   - RD-19 asserted the backend sweep must reach **0** references, after RD-18 had established
+     that a reference inside a path to a document that still exists is a pointer, not
+     provenance, and exempted one. The supervisor did not run that check against `backend/`.
+     Two such paths existed. The target of 0 gave the agent no way to keep them, so it
+     described the two documents in prose instead — losing a path that resolved. Fixed
+     afterwards; the target is 2. **When a ticket repeats an earlier sweep, re-run the earlier
+     sweep's exemption check against the new scope.** An exemption is a property of the
+     content, not of the directory that happened to hold it first.
+
    Four habits that prevent all five:
 
    - **Use `git grep`, not `grep -r`.** It searches tracked files only, so untracked and