notes(05): sync title and blurb with Feishu time-placement arc

Match the polished article: how the agent learns current time; history
write-once for <agent-context>; README title aligned.

Author: hetao

notes/05-prefix-cache.md

@@ -3,9 +3,10 @@
 **In one line:** the model has no clock. Stuffing `date` into the system
 prompt is the most direct fix — and it breaks the prefix cache every turn.
 Put session-stable `# Environment` up front; put per-turn time in
-`<agent-context>` that is never rewritten; keep precision to the minute.
-For each injected part, ask what breaks without it, whether it needs every
-turn, how precise it must be, and whether its position breaks the prompt cache.
+`<agent-context>` that is written into history and never rewritten; keep
+precision to the minute. For each injected part, ask what breaks without it,
+whether it needs every turn, how precise it must be, and whether its position
+breaks the prompt cache.
 
 **Companion skill:** `context-tax-audit` - inventory one real request, then
 check necessity, frequency, precision, position and cache impact.

notes/README.md

@@ -10,6 +10,6 @@ repository holds something you can install and run for it.
 | 02 | [Too many tools will eat your context: from tool search to PTC](02-tool-context.md) | `tool-budget-audit` |
 | 03 | [Keeping long sessions sharp: compaction vs. memory](03-compaction-memory.md) | `long-session-check`, `handoff-doc` |
 | 04 | [How long should one bash command wait: from foreground blocking to background tasks](04-bash-background.md) | `long-command-check` |
-| 05 | [One small field can break the whole prefix cache](05-prefix-cache.md) | `context-tax-audit` |
+| 05 | [How does the agent know the current time?](05-prefix-cache.md) | `context-tax-audit` |
 
 All companion skills live in [`stacks/ronny/skills/`](../stacks/ronny/skills/).