fix(agents): avoid injecting memory file twice on case-insensitive mounts (#26054)

* fix(agents): avoid injecting memory file twice on case-insensitive mounts

On case-insensitive file systems mounted into Docker from macOS, both
MEMORY.md and memory.md pass fs.access() even when they are the same
underlying file. The previous dedup via fs.realpath() failed in this
scenario because realpath does not normalise case through the Docker
mount layer, so both paths were treated as distinct entries and the
same content was injected into the bootstrap context twice, wasting
tokens.

Fix by replacing the collect-then-dedup approach with an early-exit:
try MEMORY.md first; fall back to memory.md only when MEMORY.md is
absent. This makes the function return at most one entry regardless
of filesystem case-sensitivity.

* docs: clarify singular memory bootstrap fallback

* fix: note memory bootstrap fallback docs and changelog (#26054) (thanks @Lanfei)

---------

Co-authored-by: Ayaan Zaidi <hi@obviy.us>

docs/concepts/system-prompt.md

@@ -59,7 +59,7 @@ Bootstrap files are trimmed and appended under **Project Context** so the model
 - `USER.md`
 - `HEARTBEAT.md`
 - `BOOTSTRAP.md` (only on brand-new workspaces)
-- `MEMORY.md` and/or `memory.md` (when present in the workspace; either or both may be injected)
+- `MEMORY.md` when present, otherwise `memory.md` as a lowercase fallback
 
 All of these files are **injected into the context window** on every turn, which
 means they consume tokens. Keep them concise — especially `MEMORY.md`, which can