Everything else attaches to it.

Same eight concepts, four properties each. Read across a row.

Concept	Origin	Per session	Cross-project	Shape
Sessionatom One conversation. Immutable UUID.	Auto	One per session	Not applicable	None
Project Derived from the working directory.	Auto	One per session	Not applicable	None
Alias Human-readable nickname for a session.	You create it	One per session	Not applicable	None
Tag Flat #keyword labels.	Auto or manual	Many per session	Yes	Flat
Collection Hand-picked tree, up to 8 deep.	You create it	Many per session	Yes	Tree (8 deep)
Thread DAG of sessions tied by intent.	Auto or manual	Many per session	Yes	DAG
Pin Floats a session to the top of its list.	You create it	One per session	Not applicable	Single star
Note Markdown attached to a session.	You create it	One per session	Not applicable	None

Which concept fits the moment?

If Same concept appears across many sessions?

Tag it

e.g. #auth · #migration · #bug-fix

If A handful of sessions for one milestone?

Make a Collection

e.g. v1.0 launch decisions

If One particular session to recall by name?

Alias and pin it

e.g. auth-middleware-refactor

If Several sessions form one unit of work?

Spin up a Thread

e.g. planning + execution children

How things are organized

The diagram above maps every concept onto the Session atom. The matrix:

Concept	Auto / manual	Per-session	Cross-project	Hierarchical
Project	auto from `cwd`	one	–	no
Alias	manual	one (history kept)	n/a	no
Tag	manual or auto-scan	many	yes	flat
Collection	manual	many	yes	tree, max 8 deep
Thread	manual now, auto in v0.15b	many	yes	DAG
Pin	manual	one (boolean)	n/a	no
Note	manual	one (history kept)	n/a	no

#Which one when