feat: dynamically resolve AGENTS.md files from subdirectories as agent explores them

[rekram1-node]

No description provided.

[rekram1-node]

/review

[github-actions]

lgtm

[rekram1-node]

/review

[github-actions]

lgtm

[xHeaven]

@rekram1-node if an agent reads several files in one go in a directory that has AGENTS.md files, it'll load them multiple times because deduping only considers instructions that were loaded by previous completed tool calls in ctx.messages. If there are multiple read calls in the same assistant step, each read gets the same ctx.messages.
This only happens when the agent goes into directories that it hasn't explored yet.

Visual:

root
├── frontend
│   ├── file1
│   ├── file2
│   ├── file3
│   └── AGENTS.md
├── backend
│   ├── file1
│   ├── file2
│   ├── file3
│   └── AGENTS.md
└── AGENTS.md

User: read 3 files in the backend directory
Agent: sure dude, lemme check

✱ Glob "backend/*" (4 matches)
→ Read backend/file1
↳ Loaded backend/AGENTS.md
→ Read backend/file2
↳ Loaded backend/AGENTS.md
→ Read backend/file3
↳ Loaded backend/AGENTS.md

User: read those files again
Agent: i've done it already but ok

✱ Glob "backend/*" (4 matches)
→ Read backend/file1
→ Read backend/file2
→ Read backend/file3