Imported from fourcolors/luna (seeds/skills/subagent-memory/SKILL.md). Install upstream with npx skills add fourcolors/luna --skill subagent-memory. Copyright stays with the author.

Subagent observational memory

You have a persistent memory directory because your agent definition declared memory: project, memory: user, or memory: local. The harness has already injected the first 200 lines / 25KB of MEMORY.md into your system prompt.

This skill defines an observational memory discipline: at the end of each invocation you extract observations about what just happened and append them as dated bullets. When the file approaches the 200-line cliff, you compress it by running a reflection pass. The pattern mirrors the project-level working_memory skill — same bullet syntax, same priority emoji, same append-then-reflect rhythm — adapted for a subagent observing its own task.

When this skill applies

Four moments in your invocation:

1. At task start — re-read your MEMORY.md (already in your system prompt) with the current task in mind. Anything relevant?
2. Mid-task, when something surprises you — make a mental note. Don't break the task to write.
3. At task end, before returning your summary — run the observer pass to extract observations, append them to MEMORY.md.
4. Right after appending — count lines. If MEMORY.md is ≥ 195 lines, run the reflector pass to compress to ≤ 100 lines.

If a particular invocation has nothing observation-worthy (trivial lookup, repetition of work already captured), output the equivalent of <no-new-observations/> to yourself and skip the append. Don't write filler.

File layout

Your memory directory contains exactly one file:

.claude/agent-memory/<your-name>/
└── MEMORY.md

There are no topic files, no frontmatter on entries, no index. The whole file is observations grouped by date. The harness reads the first 200 lines / 25KB at startup; reflection keeps you well below that cliff.

A populated MEMORY.md looks like this:

# Subagent observations: codebase-analyzer

Date: May 5, 2026

* 🔴 (14:30) Webhook retry logic lives in WebhookHandler, not per-provider modules — centralized after Stripe outage 2026-Q1
* 🟡 (14:31) Webhook max_attempts read from :webhook_max_attempts config, not Oban.Job.max_attempts — custom backoff reads at insert
* ✅ (14:35) Located retry handling at lib/my_project/webhook_handler.ex:42-78

Date: May 3, 2026

* 🔴 PropertyRepo.with_property/3 is the only safe path to multi-tenant data — RLS requires it
* 🟡 Phoenix LiveView assigns flow through assign/3 — never mutate socket.assigns

Observation format

Each observation is one bullet under a Date: <Mon D, YYYY> header. Bullets start with a priority emoji (or completion marker), an optional (HH:MM) 24-hour timestamp, and the content. Indent sub-bullets with → to group tool sequences.

Date: May 5, 2026

* 🔴 (14:30) Critical lesson — must know for next invocation
* 🟡 (14:31) Useful project fact or tool outcome
* 🟢 (14:32) Minor detail or low-confidence observation
* ✅ (14:35) Concrete task milestone reached
  * → ran grep for "webhook_handler" in lib/, 3 hits
  * → read lib/my_project/webhook_handler.ex:42-78
  * → confirmed retry logic centralized here

Priority emoji

Adapted from working_memory for subagent context (you observe your own task, not a user conversation):

• 🔴 critical — hard constraints, gotchas with concrete consequences, parent-agent corrections, decisions that change how future-you should approach similar tasks. The "if I forget this, I'll repeat the mistake" tier.
• 🟡 useful — project facts (file paths, line numbers, config keys, commit SHAs, external IDs), tool results worth remembering, patterns observed in the codebase. The "this would save me time next invocation" tier.
• 🟢 minor — low-confidence observations, ambient context, things you're not sure are worth keeping but might be. The reflector will probably drop these.
• ✅ completed — a concrete sub-goal of the task was achieved with a result worth recording (located a file, confirmed a behavior, ruled out a hypothesis). NOT used for "the task is done" — that's implicit.

Good vs bad observations

GOOD: 🔴 (14:30) Webhook retry config key is :webhook_max_attempts in config/<env>.exs, not Oban.Job.max_attempts
BAD:  🔴 (14:30) Found something about webhook retries
        ^^ vague, no actionable detail

GOOD: 🟡 PropertyRepo.with_property/3 must wrap multi-tenant queries — RLS enforces; bypassing causes silent cross-tenant reads
BAD:  🟡 Multi-tenancy is important
        ^^ generic, derivable from CLAUDE.md, no value-add

GOOD: ✅ Located handler at lib/my_project/webhook_handler.ex:42-78 (Oban worker with custom backoff)
BAD:  ✅ Did the task
        ^^ no information, no future value

Reading memory (at task start)

Your MEMORY.md is already in your system prompt — re-read it with the current task in mind. For any observation that looks relevant:

• Verify named things still exist. An observation that names a file path, function, line number, or flag is a claim about a moment in time. Before acting on it, grep or file-check. "The memory says X exists" is not "X exists now."
• If observations conflict with what you observe in the current code or tool output, trust what you observe. Then mark the stale observation for correction (you'll fix it during the observer pass at task end).
• If MEMORY.md looks truncated or malformed at startup (a prior invocation may have died mid-reflection), run the reflector pass immediately before doing other work. Recovery is cheap; acting on a half-file is expensive.

The observer pass (at task end)

Before returning your summary to the parent agent, extract observations from what just happened. Treat yourself as the memory consciousness of your future self — these observations are the only memory of this invocation that future-you will have.

What to observe

• Surprises: anything that violated your expectation. Why was it surprising? What's the underlying mechanism? (→ usually 🔴)
• Concrete facts you discovered: file paths, line numbers, function signatures, config keys, identifiers in external systems. (→ usually 🟡)
• Parent-agent feedback: corrections become 🔴 (must follow next time); confirmations of non-obvious approaches become 🔴 (validated discipline).
• Tool sequences that produced a result: group as a parent ✅ with → sub-bullets for the steps. Future-you cares about the outcome, not the keystrokes.
• Decisions you made between two reasonable options: record which you picked and why, so the next invocation doesn't re-debate. (→ 🔴)

What NOT to observe

• Restatements of CLAUDE.md, the project README, or anything you could re-derive by reading current code or git log.
• Generic best practices ("good code is readable").
• Bookkeeping ("I started the task," "I finished the task").
• Repetition of observations already in MEMORY.md — check first; update an existing bullet rather than add a duplicate.
• Internal reasoning steps that didn't produce a load-bearing decision.

Output discipline

• 1–5 observations per invocation. Fewer is better than more. If you wrote 8 bullets, three of them are probably 🟢 noise — cut them.
• Be specific enough to act on. "User prefers terse responses" beats "user has preferences." Include the why if it's non-obvious.
• Use terse language. Dense sentences. No filler words. The token budget is finite.
• Group related sub-steps as one parent bullet with → indented children. A parent ✅ with three sub-bullets > three separate ✅s.

Append, don't replace

Find today's Date: header. If it exists, append your new bullets under it. If not, add a new dated section at the bottom of the file. Never delete or rewrite existing bullets during the observer pass — that's the reflector's job.

The reflector pass (when MEMORY.md ≥ 195 lines)

After appending new observations, count lines in MEMORY.md. If ≥ 195, you must compress before returning. The harness's startup injection is hard-capped at 200 lines; without reflection, the bottom of the file falls off invisibly.

The compression target

Reduce to ≤ 100 lines. This gives ~95 lines of headroom for future invocations to append before reflection fires again. Don't aim for "just under 195" — that means reflection fires every invocation, which is wasteful and slowly degrades signal as borderline observations get repeatedly re-judged.

Preservation rules — always keep

• All 🔴 observations that name hard constraints the parent agent or codebase imposes (corrections, conventions, gotchas with consequences).
• 🟡 observations that name hard-to-rederive facts: file paths, line numbers, commit SHAs, config keys, external system IDs. Re-deriving these costs tool calls; preserving them is cheap.
• ✅ observations from the last 7 days (recent completions are still "current state").
• Anything naming a gotcha or root cause — these are the highest-value memories because they prevent re-encountering the same surprise.

Preservation rules — aggressively merge

• Multiple 🟡/🟢 bullets describing one tool sequence → one parent bullet with sub-bullets summarizing the outcome.
• Repeated observations of the same fact across multiple dates → keep only the most recent statement.
• Successive ✅ completions belonging to one larger task → single rolled-up ✅.

Preservation rules — drop

• 🟢 observations older than 7 days with no enduring value.
• ✅ completions older than 14 days that are now superseded by newer state.
• Bookkeeping observations that don't record a decision.
• Empty, redundant, or contradicted observations (newer wins).

Format after reflection

Same structure: Date: headers, priority-emoji bullets. Drop (HH:MM) timestamps when merging across times — they only matter at original capture. Group bullets under their dates; if you collapse multi-day entries, keep the latest date for the rolled-up bullet.

Validation

After running the reflector, count lines again. If the result is not ≤ 100 lines, your reflection wasn't aggressive enough — drop more 🟢 entries, merge more sequences. If the result is < 30 lines, you over-compressed and lost signal — restore from the pre-reflection state and re-do with less aggression.

If after honest reflection the file is already as tight as it can be (less than 20% reduction possible), leave it as-is and add an observation noting that you tried. The next invocation will reach the threshold sooner and you'll try again with more accumulated context to drop.

A complete worked example

You're a codebase-analyzer subagent invoked with: "Find where we handle webhook retries."

At task start

You re-read your MEMORY.md (already in system prompt). You spot:

* 🔴 Webhook retry logic centralized in WebhookHandler after Stripe outage 2026-Q1 — not in per-provider modules

You verify the file exists with ls lib/my_project/webhook_handler.ex. Confirmed. You skip the per-provider modules and go straight to the central handler. The observation saved you ~5 minutes.

Mid-task

Reading webhook_handler.ex, you discover the retry count is set via Application.get_env(:my_project, :webhook_max_attempts), not Oban's standard max_attempts field. The custom backoff function reads this config at insert time. Surprising — you'd expected the standard Oban field. This is a gotcha worth saving.

You also locate the precise lines (42–78) handling the retry logic.

Observer pass (at task end, before returning summary)

You extract three observations:

Date: May 5, 2026

* 🔴 (14:30) Webhook max_attempts read from :webhook_max_attempts config key, NOT Oban.Job.max_attempts — custom backoff reads at insert time
* 🟡 (14:31) Webhook retry handler at lib/my_project/webhook_handler.ex:42-78
* ✅ (14:35) Confirmed retry logic centralized in WebhookHandler (matches prior observation)

You read MEMORY.md, find today's Date: header (or add one), append the three bullets.

Threshold check

You count lines: MEMORY.md is now at 47 lines. Well under 195. No reflection needed. You return your summary to the parent agent.

A later invocation: reflection fires

Several invocations later, MEMORY.md has grown to 198 lines after a particularly observation-rich task. You count lines, see ≥ 195, and run the reflector pass.

You apply the rules: keep all 🔴 hard constraints, keep 🟡s naming file paths and line numbers, drop 🟢s older than 7 days, merge three separate ✅ bullets from yesterday's exploration into one rolled-up ✅. The compressed file is 87 lines. Within target.

You replace MEMORY.md with the compressed version and return your summary. The next invocation starts with a clean, dense memory and ~108 lines of headroom before the next reflection.