# M5a task 17: `memoryd` takes the day and the month with `get`, not by slicing

**Branch:** `m5a` (run `git switch m5a`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `memoryd: the day and the month of a time with get, never a slice`

## Goal

No behaviour change. Four files of `memoryd` cut the day (`2026-09-24`) or the month (`2026-09`)
out of `to_rfc3339()` with a slice such as `&rfc[..10]`. `AGENTS.md` forbids indexing that can go
out of range in library code. The time is always long enough, so none of these can panic today,
but two of them rely on that without a check. All five places become `str::get` with a fallback,
which cannot panic whatever the string is. Found in the M5a review (2026-09-24).

## Files

- Modify: `crates/memoryd/src/notes.rs`, `crates/memoryd/src/journal.rs`,
  `crates/memoryd/src/review.rs`, `crates/memoryd/src/recall.rs`, `docs/implementer-log.md`
- No test changes: the existing tests cover every line changed.

## The edits, exactly

Nothing else in these files changes. Leave the comments above each line as they are.

**1. `crates/memoryd/src/notes.rs`**, in `minute`, the two lines

```rust
    let head = if s.len() >= 16 { &s[..16] } else { &s };
    format!("{head}Z")
```

become the one line

```rust
    format!("{}Z", s.get(..16).unwrap_or(&s))
```

**2. `crates/memoryd/src/journal.rs`**, in `append`, the five lines

```rust
    let day = if rfc.len() >= 10 {
        &rfc[..10]
    } else {
        "0000-00-00"
    };
```

become

```rust
    let day = rfc.get(..10).unwrap_or("0000-00-00");
```

and, further down in the same function, the line

```rust
    let month = &day[..7];
```

becomes

```rust
    let month = day.get(..7).unwrap_or("0000-00");
```

Leave `&all[all.len().saturating_sub(count)..]` in `log` as it is: its start is never past the end.

**3. `crates/memoryd/src/review.rs`**, in `submit`, the line

```rust
    let day = &rfc[..10];
```

becomes

```rust
    let day = rfc.get(..10).unwrap_or("0000-00-00");
```

**4. `crates/memoryd/src/recall.rs`**, in `recall`, the line

```rust
    let month = &rfc[..7];
```

becomes

```rust
    let month = rfc.get(..7).unwrap_or("0000-00");
```

## Steps

- [ ] **1. Make the five edits.** Run `cargo fmt --all`.
- [ ] **2. Check none is left.** `grep -nE '\[\.\.[0-9]+\]' crates/memoryd/src/*.rs` prints
  nothing.
- [ ] **3. Run the tests.** `cargo test -p memoryd`: every suite passes.
- [ ] **4. Run the gate.** `make gate`. Expected last line: `gate: ok`, with 936 tests, the same
  as before this task.
- [ ] **5. Log and commit.** `git add crates/memoryd docs/implementer-log.md && git commit`

## Done when

- `make gate` prints `gate: ok`, and step 2's `grep` prints nothing.

## Stop and report if

- Any line quoted above is not in the file exactly as shown.
- Any test fails. This task changes no behaviour, so a failure means an edit is wrong; do not
  change a test.