Does the position of an earlier file read in context matter — is denying a later re-read of the same file a mistake?

[jayakumarn]

🏷️ Discussion Type

Question

💬 Feature/Topic Area

Copilot Agent Mode

Body

Does the position of an earlier file read in context matter — is denying a later re-read of the same file a mistake?

Hi 👋 I'm using a preToolUse hook on Coding Agent — to cut token use in long agent sessions. I've got the correctness cases covered, and I'm left with one question about context behaviour I can't answer from the outside.

What the hook does

When the agent re-reads a file it has already read, my preToolUse hook denies the read (permissionDecision: "deny") with a reason saying the file is already in context. That avoids re-sending the file to the model and saves tokens.

So the only case my hook denies is: the file is unchanged and still in context.

What I already handle

• File edited → I clear the cache entry, so an edited file is always re-read. I never serve a stale version.
• Context compacted → I clear the cache on compaction, so I never tell the agent “you already have this” after the content has actually been dropped from context.

The case I'm unsure about

Here's a concrete example. The agent reads some file — call it config.py — early on. Many turns of other work go by. Then, for a different purpose than the first read, it reads that same file again. It hasn't changed and hasn't been evicted, so my hook denies it.

My worry: the earlier copy is now sitting far back in context, and models attend less reliably to content deep in a long context ("lost in the middle"). So the re-read might be the model deliberately pulling the file forward for its current task — not a redundant repeat. If so, denying it could quietly degrade the result even though nothing is technically missing.

Questions

1. Does read position matter? When a file was read many turns ago but is still in context, is a fresh re-read treated as redundant, or does re-reading meaningfully help by placing the content near the model's current reasoning? Put plainly: is denying a far-back re-read of unchanged content safe, or is it a mistake?

2. Is a repeat read a deliberate signal? Does the agent tend to re-read a file only when it actually needs the content foregrounded for its current step — in which case a deny works against it?

3. Context position in the hook input. Does the preToolUse JSON expose anything I could use to make this call — current context size, token counts, or how far back a previous read sits? I only see toolName, toolArgs, sessionId, timestamp. If there's a way to tell an earlier read is still near the front vs buried deep, I'd deny only in the “still near the front” case.

4. What the model sees on deny. When preToolUse denies a read, is permissionDecisionReason fed into the agent's context as feedback it reasons over, or is it only shown to the user / logs?

Already checked

The hooks docs and reference. Happy to share the hook script or a small repro. If the honest answer is “don't deny re-reads at all,” that's useful to know too.

Thanks!