[vincentchoqueuse]

Two changes, both closing gaps between what the library says and what the reader expects.

taps becomes observations

The retained-signal mechanism of Sequential is renamed after what it is: an observation is simply the output of a named mechanism, explicitly retained for experimental analysis. It performs no computation and does not alter the signal — same shape, same dtype, dimensions never reduced; power, SNR or SER stay with the metrics, applied to the observation afterwards.

• Sequential([...], observations=["tx"]) declares what to retain; chain.observation("tx") reads it back after the run.
• Observation names are the block names already used by set_params, wiring and the profile table — no new naming system.
• Renamed with it: tapped_ → observed_, the "taps" key of graph() and of the JSON export → "observations", the tapped mermaid class → observed; wiring sources are now "observed automatically".
• An empty observations list retains nothing, so large batches and fibre propagations pay only for what they declare.
• The FIR sense of the word (filter taps, channel taps, TappedDelayLine) is untouched.
• Vocabulary swept through docstrings, CONVENTIONS.md, ARCHITECTURE.md, README, all tutorial and getting-started pages, examples (figure titles regenerated), validation scripts and the tutorial skill; tests/core/test_taps.py becomes test_chain_observations.py.

One breaking-change window, no compatibility layer (D9): taps=/tap() are gone.

QPSK carries the pi/4 offset of the standards

get_alphabet("PSK", 4) sampled the raw circle exp(2j*pi*m/4): points on the axes, a constellation rotated by pi/4 from the QPSK of the standards (3GPP, 802.11) and of every textbook figure. QPSK now sits on the diagonals — the same point set as QAM-4. BPSK and M ≥ 8 keep the phase-0 convention.

Rotation changes no error rate (mapper and demapper share the alphabet, the noise is circular), but it removes the pi/4 surprise against any other tool, and the tx-PSK/rx-QAM mixing trap whose points landed exactly on the decision boundaries.

• The historical-table pin of tests/core/test_alphabet.py asserts the one deliberate deviation as the relationship it is: built = table × exp(j*pi/4), labelling untouched.
• The Gauss–Hermite accuracy table of capacity.py is re-measured for the diagonal orientation (1.9e-5 bit at 40 nodes — the node grid is axis-aligned, so the quadrature error is not rotation-invariant even though the capacity is).
• The Alamouti and MIMO pages are re-pasted from one fresh run each (their Monte-Carlo tables shift in the third digit — same noise draws on rotated symbols) and the constellation figures turn by 45°; the MIMO cost block also catches up with the script's actual output. The PAPR and PDM pages are re-checked and unchanged to the digit.

Verification

• 1200 tests + 1225 subtests green (doctests included), examples smoke tests green
• ruff check . clean, pyright 0 errors, sphinx -W clean

🤖 Generated with Claude Code

https://claude.ai/code/session_01Pn2F8X4HZhS8fEJcL5enzw

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